The one thing I have found is, it's tough to be out of tune on a fretless if you have any kind of ear. I'm speaking of during a gig, and slowly by sound finding a string out of tune. (Mostly flat). A slight adjustment with your fretting hand while playing can fix that. No one typically notices except the player if its minor. Sometimes an inexperienced fretless bass player misses it as well if not into what they are actually putting out. Hard to make that same adjustment on the fly with a fretted bass if there isn't a tuner in line. You can hear it but, until a song is over you can be stuck with "out of tune". I love my fretless' but, I really appreciate my fretted basses as well.