My suggestion is, even if snap to grid is on, you can hold down right click and move an object or piece of terrain around freely without it snapping to the grid. This wouldn't toggle snap to grid off, however it would bypass whether snap for grid is on while right click is held down. This could be useful for instance if you used snap to grid mode, but had to align the trigger area of an object precisely and didn't want to turn it off just to turn it on again in a few secs.
