As much as I pretend otherwise, it is probably the case that most people drink coffee for the caffeine. They view it not as a drink to be enjoyed, but more as an energy supplement to be used for its utilitarian value. That's fine.
I understand that life, for many, is characterized by a constant state of sleep deprivation, poor eating habits, and other factors that lead to fatigue. But life goes on, whether you're being dragged, or doing the dragging. Caffeine can help you do the latter.
I've blogged, earlier, on caffeine's merits as brain fuel. Specifically, how it can help students study longer, and with more focus than they might otherwise manage. But frankly, that's not caffeine's most relevant purpose for me, student though I technically am.
No, I value caffeine more for its endurance boosting properties. As in working out. Seriously, grow up people.
There is science to support this. I won't quote it, or even link to it, but you can find studies with a quick search. I simply want to keep this as straightforward as possible.
Thus this, in the most succinct terms I can muster, is what caffeine does for you, relative to endurance: First of all, it literally does extend the ability of your muscles to perform aerobic work. But, perhaps more importantly, it lessens the perception of effort. That is, you feel like you can run harder, so you're more likely to do so. It also, a bit surprisingly, leads to quicker recovery, so you can hit the road the next day.
Typically, it takes about an hour for caffeine to really peak. Which is nice, because an hour is about the closest to a race you really want to be drinking anything (excepting, of course, long runs which require hydrating on the move). What's more, the effects last 4-5 hours, which ought to be enough time for you to finish anything marathon length or shorter.
Also, contrary to popular belief, coffee consumption leads to a net water gain. Its effects as a diuretic are vastly overstated. In fact, coffee isn't significantly (in the actual scientific sense of the word) more a diuretic than plain water.
Another excuse to drink coffee? You bet.