You shouldn't train to failure every session though. Its hard on the CNS, and you'll end up having to take a week off from training sooner, rather than later.
Training to, or past failure (with a partner of course) is one of those 'occasional' techniques you use to trigger new growth. "Normal" training is sufficient to trigger growth as the body wants to be able to perform physical labor efficiently. Its when you get stuck at a certain poundage that you should pull out the so-called 'advanced' techniques like negative reps, forced reps, drop sets, etc.