He read that 2 minutes is the ideal rest time between sets in the gym, and he wants to get it exact. Once that watch beeps at the 2 minute mark, he'll be back in the squat rack to perform another set. He stands up tall and paces around trying to catch his breath in preparation for his next battle with the weights.

Time is up. His still feel weak and his heart is still beating a lot, he doesn't feel completely ok, but the watch beeped and that means his has to go back and perform another set, it does'nt matter how he feels.

He performs the next set. He is not really ready to exercise right now, so he puts forth a mediocre effort, finish the set, and waits for another 2 seconds. He is making a huge mistake, just as hundreds of lifters in another gyms.

Working out in this way is really far from efficiency. His effort level is far less than his maximum potential. If he doesn't change the way he trains, he will sacrifice a great ammount of muscle growth.

Muscles grow because of an adaptive response to stress. You lift X amount of weight for Y number of reps, and your body adapts to this level of stress. In order to see continual gains in muscle size, you must continually force X and Y to higher and higher levels.

It's quite simple: it's about lifting as much weight for the greatest number of reps that you possibly can. And repeat, and repeat, and repeat...

Because of this, you must always go into every single set of every single workout at your maximum strength potential. By sacrificing the amount of weight you can lift, you sacrifice the amount of muscle you can build. And there is no worse way to make this sacrifice than by not providing your body with enough rest between sets.

A watch will never tell you when you are ready to begin the next set. Instead of it, listen to your body and you will know when to follow your training.

A deadlift and a tricep pressdown aren't exactly in the same boat here. After a heavy set of deadlifts to failure I'll usually be resting for at least 5 minutes, often even more. A set of tricep pressdowns is obviously not as taxing and may only require a rest period of 2.5 minutes for me to feel fully recovered.