I started out multiboxing when tbc. My one of my reasons was maybe a bit different from others. I was horde, and I knew my guild would need paladins in near future. However I had previously played a shadowpriest as main, and could not really let go of this amazing role.

Therefore I decided, why not run everything and more:P Hence I made my paladin and 4 shadowpriests (who later became holynukers).

However I was growing bored of grinding the same instances again and again when I hit 70. I therefor decided to do some pvp. But for pvp I found that I had one big problem; the protection paladin. This was totally useless for pvp-purposes. I could go with 4 priests, but not really a an option for me.

The real strenght of multiboxing(and also weakness) is AoE damage. Therefor I decided to make my new team of 1 shaman and 4 locks. Later one I discovered that shaman and warlocks did not really run very well together, because warlocks were mobile, but shamans were not.

At 60 I switched out the shaman for a priest I allready had at that level. I now really love my priest/4xlock team for BG and world pvp. However I got really run over in arena.

Shamans however has better survivablity and semi-aoe with high damage. This is perfect for arenas. However then again, I think shamans would be less effective in a mobile enviroment as AV. Not useless however, but I still think mobile locks would be better in BG's

My point is that there is very different group compositions you should have to do different things when you hit 70. Therefor I've decided to try some more things.

I allready have my lvl 70 pally +4xpriests and 1xpriest+4warlocks. Now its time for trying out 5 shamans and we'll see if I get them also to 70 before wotlk releases :P I'm getting a bit bored of levling, but its fun to try out different group compositions.