@MissCourt - A perfect game example of graticule grids is Dungeons and Dragons. Every map is designed on a grid so that you can move your character around and judge distances for spells and attacks. Since most computer and video games are based off of Dungeons and Dragons, of course they would want to use a grid system. You can take a Dungeons and Dragons map and enter it directing into the computer just by numbering the grid boxes.
You forgot to mention it, but the military also uses their graticules to measure the size of targets and landscapes. Just like a game boss takes up four squares, a target might take up multiple squares.