I work out at home, alone. I prefer it that way. Mostly for a lot of the same reasons that have already been mentioned. I do, however, miss out on getting those last couple reps past failure. For now, I lift until I know that was the last rep. If I happen to push it beyond, and get stuck, usually twisting, turning and arching gets it back to the rack. I just don't count that as a rep.
.02,
Joker