Kicad has some pre defined grids. But in ecad programs it makes sense not to limit the user to some set of pre defined grids.
So has been introduced another user set-able grid. The user grid.
The user grid is extremely useful. As kicad is more or less a direct cad program. Without the console where you can enter relative coordinates.
Weird grid spacing are very useful for footprint creation. Have a look at my new tutorial to see how this can be done: Tutorial: How to make a footprint in KiCad 5.1.x?