Should bodybuilders train with, without or in a variety with pre-exercise supplements?

Pre-exercise will lead to better performance in training (for instance weight lifted) but to less stress on muscles (or could lead to...). Would it be adviced to vary this so sometimes the muscle will have more stress related to certain training markers, and this leads to more results in the long run?

Regarding to competitions they should train with pre-exercise supplements in the last week before competition.