I train to strict failure meaning I could cheat out a couple more reps but stop right there. Your last rep should be difficult to complete, but should not require an all out effort and cheating. Bodybuilding is all about knowing your personal zone. If you train and quit the set too early, nothing happens. If you go too far, and push beyond, your body shuts down (maybe it's a protective mechanism) you might start shrinking and looking terrible. Find the zone. I call it 85% - 90% training. 0% - 75% won't get you much. 90% - 100% can have you going in reverse gear. In the end, the truth is in the pudding. Either you are gaining and have muscle and energy or don't. All the talk in the world doesn't change that.