Multi-class setups are possible. you just have to arrange yuor macros/keybinding to make them work for the group. Multi-class takes more coordination and understanding of each class abilities.

Same class setups allow for easier to configure macros.

I have a 5 shaman team and I enjoy the versatility of the group in the sense that I can rez team members, self rez(wipe protection), dps, heal, half-ass tank/melee. I already had a lvl 70 elemental shaman on Lightbringer and enjoyed it more than any of my other 70's. So I wanted to play a class that was fun for me.