Why is it sometimes you see people resting for 2 minutes between each exercise, and sometimes they only rest for 30 seconds? The answer is that they have different goals. When you’re lifting really heavy weights (like body builders) your muscles need more time to rest before they can go again, so this is why you see big guys hogging the bench press for half an hour. Those looking to shape muscles and trim some fat will rest for much shorter periods of time, which is why you often see women resting for 30 seconds or less. The goal in both scenarios is to lift as much as you can, in good form, for the number of reps you wish to do.  Neither way is good or bad, they are just different and dependant on your goal.