Here's another reason to keep moving in the gym.  Conditioning Research sites a study that shows more growth hormone is secreted if you take shorter rests between sets of exercises.  About 30 second rests are optimal and can be achieved easily through circuit training.   

Thus, the magnitude of acute GH responses in previously strength-trained women appears greater with a 30-s rest interval between sets compared to longer rest periods of 60- or 120-s.

This is another great argument for intensity and how my move it or lose it mentality wins hands down against sitting on your butt between sub maximal sets. 

Those who work hard, move swiftly, and execute powerful exercises during their workouts are the ones who make every repetition count toward their goals in minimum time.  Those are the folks who win!