Well, it's really like physical exercise. It's not a question of either/or, it's doing both. You would not exercise all the time, nor would you rest all the time. They are the separate components of a complete cycle. You exercise, then rest, exercise, rest.

Exercise is the physical stimulation that drives the body to higher levels of performance. But you still very much need rest for the rebuild part. Catabolism + anabolism = the complete metabolic cycle.