I just noticed that the grid subdivision parameter doesn't subdivide grid cells: it actually groups cells together and changes the look of intermediate lines. I.e. if you create a 64*64 grid and set the subdivision to 3, the main grid lines will be 192 pixels away from one another. I'd expect it to work the other way around. That's how it is in Photoshop, which just places the subdivision lines at regular intervals (even if some end up on sub-pixel positions, in the example 21.3px away from one another).
The main use I've found for subdivisions is to find the center of my grid cells (for tilemaps/character sprites for games). I can't imagine a use for the current way it works. But if you decide to keep it, I think it would need a more representative name, like "group cells".