Assume you have an object 10.5mm long. If I set the system to snap to 1mm and then stretch the object on the edge that is on the 0.5 grid, it will start snapping at 10.0 resp 11.0 mm, then progresses to 9/12mm. So in other words, it snaps at 0.5 initially and then at 1.0mm.
When I start stretching it at a corner that sits on the 1mm grid, it would stretch immediately on +/- 1.0mm.
I would prefer it to snap to 9.5 and 11.5 mm instead in all situations..
It seems that the snap is based on the projected grid and not on the current size of the object
Maybe those two options could be separated with holding the ALT key or a setting/checkbox next to the snap scale.