I have been a user of PhotoLab since version 1. My metadata requirements are much simpler than many others users. I have been using the most current version of PhotoLab almost every day since late 2017. I never delete the database and I have never had a problem related to it.
Mark
So, you’re not bothered if any of your non-RAW files gets corrupted when you write metadata to them? 
Don’t forget that RAW files are containers and only part of its contents is the image data block. The metadata block is entirely separate. Apart from camera manufacturers like Nikon and Canon, who already write, not only metadata, but image editing data, there are also multiple apps that have been writing metadata to RAW files for years and not once have I seen a report that folks files have been damaged.
Like all the best apps, I use ExifTool, which has proved itself time and time again.
The main benefit of writing directly to RAW files is that I can use Apple’s Spotlight search engine to directly find which images contain which keywords, etc, without having to first find the XMP files and then find the RAW files from there.
I used to think I was paranoid, but now I know they’re out to get me 
I’m not taking photos to get containers for metadata. And I experienced a couple of corrupt RAW data (not only because a converter tried to write into the file), so the image was lost - not only the rating or keyword or GPS. This kind of stuff I can get again. No matter what, each edit process including altering of RAW files is a two sided risk - the image can be destroyed as well as the metadata. The latter is expendable although not increasing the fun.
And yet, every time you press the shutter, that is exactly what you are getting.
That is all going to depend on the software you used. There are some that can get it wrong and there are the rest, which use ExifTool.
And yet, you wouldn’t hesitate to let PL (or any other app) write metadata to you non-RAW files - or aren’t they as precious? I know lt TIFF scans of LF film are very precious and yet PL5 can write directly to them.
ExifTool first creates a copy of the original file, writes to that copy and, if the write fails in any way, you will find the renamed original sat right next to the original. All you need to do is delete the corrupted new file and rename the original.
Anyway, most people with any common sense keep a backup - see @platypus comment
I love the secondary “solid state” 25KG wireless hard disk. Heavy! 
This container is filled or not by the camera when writing the picture data. Every additional editing afterwards comes at a risk of destroying something not reproducible with something expendable.
I’ve read enough threads about “wrong going” metadata synchronisation here in DxO forum to not trust an application which refuses to take responsibility of “accidentally” (by the app) destroyed images - like all other software also tries to exclude liability for what they do to my files. Liability is a big issue with all this gameboy apps - so many things can go wrong and the damage and it’s costs always lays on the user.
Name one single person who can’t print an image because it’s lacking metadata, like GPS-Data, ratings, colour labels, keywords, even exposure data. I can count millions who never heard of the term “metadata” and use their images.
What’s the value of TIFF scans? Compared to the LF negative: close to 0. If you lose the negative or had it destroyed, no TIFF scan will ever bring it back. What’s the value of metadata compared to one single beautiful image you bring back from a travel, from a place you only saw once in that light, in that weather, with the person or animal in it? Less than 0.
Metadata only have the purpose to give additional information, like the booklet of a CD or the sleeve of a long play record. The music it contains isn’t getting more or less beautiful just because that info is missing or wrong. But I would not squeeze a longplay record into a typewriter to write the titles, composers or artists on it.
And that metadata has no big value to the people of DxO and some other app companies show very clearly, else we would have less troubles.
Have you never added a colour or text tag to files in Finder? That changes the metadata in the file or folder.
As I reinforced earlier - if you have an up-to-date backup, whether that be Time Machine or a simple clone, you are never going to lose an image irretrievably. I have Time Machine running 24/7 and, if I need it, it takes less than a minute to recover a file, no matter what format.
And, once again, I will reiterate that ExifTool is astoundingly safe and I can find no reference to it having corrupted files.
Of course. But there are also loads of folks who couldn’t manage their collections without metadata, especially keywords. Just because you can’t cope with a concept doesn’t make it wrong.
When you’ve spent a week editing a scanned image, you really don’t want to lose all that effort. But, then I have a constant, real-time, backup, so I could care less about a file being corrupted.
Of course it will. With both a clone backup and a Time Machine backup as well, the chances of losing everything isn’t worth thinking about.
The value is, 20 years later, I can search my archive by keyword or tag or star rating and find an image a whole lot quicker than sifting through boxes of negative sleeves or even folders of images, looking for an image that I might or might not recognise.
But you could write on the sleeve with a pen or pencil. I have designed a label for my negative sleeves, upon which I write the exposure details, filters used, N+/- info, etc. But without an index, it still takes a long time to find the image I am looking for - but at least I don’t have to view the neg to see what the image contains. Instead, I use the metadata I wrote on the sleeve, which I can then transfer to the scanned TIFF file’s metadata.
Yes, but that’s finder, and only finder involved in that process. In PL it’s possible to lose color tags and ratings because of it’s triple strategy while at the same time not able to cope well with the essentially needed image browsers, GPS taggers.
I just experienced that PL made some of the genuine RAW files a “virtual copy” with no possibility to write metadata to anything. As well made and excellent it is to develop RAW files - anything beyond I steer clear. I don’t know why that happened, but trustworthy apps don’t do this kind of crap.
That’s a general statement which implies “the concept is okay, it’s just me who can’t cope”. I’d say, a concept is wrong for me if I can’t cope with.
If you spent a week editing one scan, I’d seriously advise to either find a better editing tool, get some help in terms of workflow practices or just hop into the darkroom and print it - not possible because of the desired size of the print, therefore the need to use an inkjet printer?
The negative or positive film is the source. Not the TIFF file. Within 5 or 10 years from now we’ll be able to get more information out of the film scan. What will you do then? How many files you own older than 50 years? And how many devices you own being able to show their content? The thing is @Joanna some people advise to copy files from older to newer media and do that repeatedly. I have ZIP disks as well as an old 40 MB (!) Syquest cartridge. But no readers for them. Sure, I could go to the computer museum and try to copy it, but would I find an app to open old Quark XPress files?
Nothing ages as fast as digital media. Your LF film will last longer than the TIFF files you generated. That might be the reason that some other people suggest to print digital images on film - as backup…
As I said, no, as I forgot to say: The value of metadata is only in terms of organisation. And 20 years from now… be careful, maybe in 20 years you just ask an AI app to find a picture you eventually just forgot to tag. Tagging is done by humans, therefore containing the possibility to fail.
Wich would be as independent from the LP as a sidecar file 
you never put a CD into the wrong case? Or an LP into the wrong sleeve? You are the one who wants to type metadata into the image file, not me 
There’s simply no guarantee that there will never occur an error in the future by constantly changing tags (for example, new keywords, new hierarchical structures, new colour labels - and always attack RAW-files with that? And a 100% check after each change? Or live with the possibility that two year ago something went wrong and the failure lived for 2 years in your backups, so you have close to no chance to correct it in reasonable time?
You are suggesting a procedure like putting the label sticker directly on your negative instead on the protective sleeve. A RAW file is no protective sleeve.
