An overly short case will end up headspacing on the extractor hook and not the chamber. That will tend to hold the case slightly cockeyed and MIGHT contribute to decreased accuracy. That being said I once put a whole box of .380 thru a 9mm just to check. I had to manually cycle the slide as the .380 did not have enough oomph to do it, but the bullet came out the end of the bore every time and accuracy wasn't unreasonably poor. Also if the case is way too short the bullet maybe won't grab properly and can come out when the slide slams the round home. That can be a bad thing. All that being said I don't remember the last time I trimmed a 9mm case to length, at least since I was making my own Makarov brass.