I use this technique a lot to add texture to the guitar sounds when playing with the band although I've never used three guitars! Varying chord shapes have such different characteristics and options that, as a band, we do this routinely. I have also got a reasonable mandolin sound out of a capo'd guitar when needed, with a bit of tweeking on the P.A.,although if possible I'd prefer to use the real thing. Sometimes, if the song has a strong, strummed ryhthm, I like to use different sounding guitars as well as different tunings. Maybe to include a classical guitar alongside a steel stringer or twelve string.