On many occasions, at gigs, other bands we've played with have asked to borrow stuff (backline the drums, amps). I never liked that. If you don't have, or can't get your gear to the gig - why are you playing? And more than once I felt I was taken advantage of - by my singer! He was like "sure, no problem" when others asked. I put a stop to that.
I did once loan my back up bass for a set, but I felt okay about him. sometimes you can tell about people. I also once lent that same bass out for a friend to do some recording - but I wasn't worried about the bass being damaged.