I find the current grid facility somewhat basic and frustrating. The grid is sized by an amount which usually yields less than a whole number of ‘boxes’. That’s all the control you’re given.
I would like to enter a percentage - e.g. 5% would yield 20 whole divisions
I would like sub divisions with a fainter line. - e.g. 4% main / 6 subdivisions would yield 24
One huge (to me) benefit is that when correcting geometry, I get a centred vertical line as part of the grid. This enables me to rotate the image to correct for verticals at the centre of the image. Then manual keystone correction will be much easier from that point.
Allow changing the grid line colour. Having it fixed does not suit all images.