Some people will take my cardio-kickboxing class and then they'll run on the treadmill for half an hour. A lot of people think that in order to lose weight, they need to do lots of cardio to burn off those calories, and they do so much they're actually overtraining. We don't know what we're doing. Some people just go to the gym and throw weights around for a few hours because they've never learned to exercise properly. We take too many breaks.
Some people take big breaks between sets.
If you're doing heavy lifting, you should rest between 1 and 2 minutes after each set. There are techniques, however, that will maximize your time. A lot of people walk to the water fountain and waste time. We enjoy the amenities too much. Obviously if your goal is to get in shape, that's a big waste of time.