That way my tech could swap out and I wouldn't have to worry about tuning.
Plus, it would be cool to have a Strat for some jangly songs, go back to a Jr for some raucous Rollin, and then whip out a LPC for the heaviest of heavy. (Heaviest of heavy for what I play- which is still probably mid-gain! )
If I'm that rich and famous I know that the audience has paid good money to attend my show and hear me play the songs that made me that rich and famous - so I play the type of guitar that provides the voicing that made any particular hit song a hit, simple as that. If I'm Neil Young I just need Old Black all night, if I'm a Beatle, I need different guitars for different song voicing's through out my career. Give the people what they came for, reward their loyalty.
I'd mostly use my Strat, but have a Tele and something with humbuckers for a couple of songs here and there, mostly for variety, but also as back ups and possibly a drop d guitar. I used to bring two to every gig, but with roadies, I could see three or four.