How do 8-mans function?

[jabbywocks]

So that'd be why for some 8-mans people recommend forming your own using PF to get 1 tank, 2 heal and 5 DPS.

I suppose. I've never had any trouble with the basic duty finder set up though. Depending on the instance, sometimes I prefer to OT rather than MT. I usually only MT if the other tank is inexperienced with the fights. I just turn off Defiance if I'm off-tanking so I can do more damage and so I'm not snaking hate away from the MT.