Im asking this because i cant find a really answer about this...

Why when you select a role in the build menu depend on the role do you get less or more HP's? I can understand that the Protector needs some more HP's, but the avenger and the sentinel why they have less HP's?

Im asking this because i tryed the avenger damage and the guardian damage in both roles and the only diferences is that the avenger do more or less 2-5% more damage... but in this role you lose 30% of your HP's? doh... then why i need a role?

For groups, mainly.

Dunno about avenger, but the support role has HUGE benefits for healing and CC, especially in terms of energy usage/regeneration. I can't even cast my rez ability unless I'm in support role, as the energy cost from maintaining it sucks me dry from full before the full maintain that is required to complete the rez. In support role and out of combat, I can maintain the rez indefinitely without a full bar of energy to start.

Also, doesn't avenger give more energy from attacks? Meaning you're sacrificing HP for faster energy build to damage with, as compared to balanced role, with the assumption being you'll be taking little/no damage with which to build up energy.