Never as pretentious as a guitarist bringing a floor rack that holds 5 at a time and they have them all sitting out.
Not exactly the case. What if said guitarist needs to play both acoustic and electric in an even proportion? In that case, doesn't it make sense to bring a backup acoustic and backup electric? Although, my guitarist just says, "Screw that, I'm just bringing the VG [and a backup electric]."
I bring my favorite bass and a backup, though I've never had to use the backup.