I figure I could go with a minimalistic UI because I doubt I know anybody on the server I am on now, so even if I get in a raid I don't give a shit what happens to any of those people.
When I am in a guild I want to know that everyone in the raid has buffs from all the palys, I want to know who is offline and who is out of range of the group, I need to see the damage I am taking to understand if I am taking too much damage, and know that I am doing the most damage I can. I need to know when and which boss abilities are incoming. On top of all that I need a UI that allows me to toss a heal, or put hand of protection, hand of freedom, hand of salvation on anybody in the raid within a second and also cleanse any debuffs, it needs to be fast so I can do all that while keeping up my rotation as ret or prot. Most paly UIs look cluttered because of being a hybrid and having very beneficial buffs.
heh I always tried to do everything a paly can do, it is what kept it interesting for me but also made my UI a nightmare, if I had a wide screen monitor I could make a much better UI, but I always knew that my UI looked like shit but I did use everything that was on the screen.