This is a legitimate method used
in weight lifting, say you are doing hack squat leg presses with heavy
weight. You get 4-5 reps and realize that it is too heavy to do more, but if
you cheat and stray from doing strict reps, you can use your hands to help
you do 3, 4, or even 5 more reps.
In doing this, it helps to completely
"shock" the muscle and you end up putting more stress on the muscle than if
you have just stopped at 4 reps. The trick to this is not helping yourself
out too much, just enough to finish the rep.
Also do this on your last set.
Works great with bicep curls, everyone has probably cheated on accident in
the beginning, but now you can explain how this is good. Use you're
shoulders / back muscles to help curl the weight up.
Be creative and try it
on other exercises. You will be surprised how this can take your training to
the next level.