"Cheating" during an exercise is your body's natural inclination to find the path of least resistance. That means your body is using its best resources to accomplish the task. To consciously fight that means more exertion from the targeted muscles and it's tough. That's why people avoid it, but that's what's required to stimulate change and get stronger. Often people get very skilled at the timing and launching of cheating and are able to stack on more weight. This is simply an illusion of strength increase.