Actually, saw a post on a forum somewhere saying a box that stuffed is a fire risk, not a badge of honor. Smushing wires like @the_john said can nick the insulation and cause a short. Best move is to turn off the power and see if you can get a slightly larger old-work box to swap in. If not, you might have to tie some wires together with a pigtail to free up space, which is a pain but safer.