Exclamation [Q] should I use task killers?

I have about 68mb free on ram and I noticed that useless apps are still running (e. g. Facebook, office suit, and other useless apps). I try to force stop them via settings but they still turn on by them selfs. Also, I think this is the reason why my battery does run out quick since theres apps runnimg in the background. Should I get a task killer e