Hindrances:
6. Cropping images sometimes only works with large jumps (e.g. at the beginning the border of the image seems to be kind of magnetic, but infinitely variable from the center onwards). The same applies to zoom in/out.
I think the magnetic frame, where the edge snaps to, has always the same width (mm or pixels) and you only recognize it as a problem, when you have to cut (or zoom) small images like logos or similar.