I always like Bill Pearl's thoughts on training to failure, some people might read it as if he is saying don't train hard but he is not, he is basically point out train hard, but train smart enough to leave something in the tank for the next workout. Like for example I can do drop sets, or push a set, not right now so much as I am coming back, but pushing a set beyond the normal range and training to what failure is are 2 different things.

Just see way too many skinny guys trying to gain weight and they do what bill advises against IMO

oh the quote which kinda says what T Joe was making the point about what Pavel is saying(I think)

People ask me why I don’t believe in training to failure at a time when the popular notion in bodybuilding is that the only way to make maximum progress is to always go for that last impossible rep (in other words, train to failure). I tell them the answer is quite simple: If you do a workout of, say, nine exercises, three sets per exercise, and in each set you go to failure, which means you couldn’t complete the last rep, what you have done in these 27 sets is trained yourself to fail 27 times! That doesn’t sound like success in my book.
My approach to training has always been to push yourself in your workouts, but do not train to failure! The last rep should be difficult, but not impossible or unachievable. And I’ve always been a great believer that you should leave the gym each day feeling like you had a great workout but you’ve still got a little bit left in the gas tank, so to speak. Because if you don’t leave the gym with the feeling of having something in reserve, you will sooner or later reach a point where your training begins to seem so hellish and burdensome, you will either start missing workouts or stop training altogether. And then where is your progress?
So speaking from experience, I urge you: Train hard, yes, but not to failure. Complete what you start — and that means every rep. I believe that this approach will not only ensure that you’ll stay with your training program year after year (obviously training longevity is a very important aspect of all of this) but you’ll also make the greatest progress. Why? Because you’ll be training yourself for success in each and every rep, set and workout. Your training will be a positive rather than negative experience. And you’ll be much more likely to keep your enthusiasm high and to avoid injury, overtraining and mental burnout.