I used to drink coffee. It has a very short-term kick, but it never kept me awake when I was truly tired, regardless of how much I drank. It's just not that powerful, at least not in my body. I have since overcome my caffiene addiction and I cannot imagine a situation where I honestly believe it would be useful. But I did not use it religiously. So for people who do, they may have trained their bodies to be awake longer if on caffiene, but certainly not necessarily so, as without caffiene, the body can remain just as aware and awake, at least in my opinion. Maybe, though, my tolerance to it had gotten so high that it didn't effect me anymore.