Once the basic skills are there and the shooter has established a basic performance level from which he intends to improve, I think you need to push to failure in order to really build new skill. I would call that an intermediate level approach to performance. And, of course, that doesn't mean work to failure every time you touch a gun; everyone needs positive reinforcement mixed in, too.
Returning to competition shooting, I can practice speeding up my draws, splits, and transitions until my end result gets more sloppy than I'd like. For match day, I need to go at (say) 90% of that failure speed, because that's what I can maintain for 8 or 10 stages and still get a satisfactory hit rate.