I can't speak to any generalities but I have seen a number of different cases in different states and involving different versions of possession violations which also involved self-defense and I have never seen the relatively minor possession charge pursued.
Mas has written up at least one of those. Not sure about the details, though I do remember it involved being on the wrong side of a state line (the good guy lived very close to the border...?)
Can't remember anything else about that one. Someone else help me out here?