I agree with Will - different keys do give different "flavours", which is very welcome to guitarists like myself who find the D/G tyranny a bit monotonous in a session.
Capos are great when playing for vocalists, but I also try to use the different major shapes whenever possible in sessions, as each has its own special characteristics. For example E major capo 3 is still G major but sounds very different. Ditto A major capo 5 instead of D. And I love it when a tune slides into a minor key, where again you get different sounds - D minor capo 2 is not the same sound as E minor.
Vive la difference, as our French cousins would say.