i dont see any reason to ever go to failure. why do it? i experience good steady gains without doing so, and i never overtrain either. i can train longer, harder, more often, with more volume, recover faster, gain strength faster, gain size faster.. all by doing volume without going to failure. at least thats my own personal experience.
If it ain't broke don't fix it.
I would never recommend someone change what they are doing if they are making consistent steady progress.
As far as going to failure is concerned, I believe there is definetely a benefit in it when done correctly. Before I get into why, I want to explain what I am talking about when I use the term failure. To me a set done to failure is when you have stopped on the last rep you were able to complete on your own with the same ROM as the first rep.. I don't mean taking a set to the point of getting stalped by the bar, having your training partner help you on the last rep, or having your form or ROM look like a different excercise than the one you began the set with.
First and foremost, you don't really know where failure is if you haven't hit that point in a while. You might think you are leaving 1-2 reps in the tank when in reality you might be leaving 3-5.
Second, when you never go to failure and your poundages are increasing it can sometimes be misleading. You may have gone from leaving 4 reps in the tank with 200lbs and moved up to 240lbs but now you are leaving only 1 rep.
Third, going to failure taxes the CNS. The body works as a unit and the CNS is a major part of it. Harness it properly and you will reap the benefits, overtax it and see how quickly your training goes to shit.
Fourth, it's not a bad thing to push yourself and know when to back off. While your body certaintly adapts and progresses from the training load you expose it to, going to failure in an intelligent way can put a sense of urgency on the whole process.