It can be very helpful with architectural images, so that you can apply the proper amount of movements to create parallel building sides (just one example). You can also consider it a multi-horizon line indicator, which can be useful for landscape imaging. If you are doing portrait imaging, you might find that the grid sort of gets in the way.
After I replaced my standard ground glass with a
Dead Link Removed, I was able to set-up my own lines on it. This came to me with a clear finish without grid lines. So using a mechanical pencil, I drew four lines on the glass to show where my Linhof Super Rollex back would crop the image (56mm by 72mm). That leaves me with two useful horizontal, and two useful vertical lines; so aligning building edges or horizon lines is still somewhat simplified over having a bare ground glass.
Ciao!
Gordon Moat Photography