I do the same. I see it as a performance enhancing drug, and as such I'd prefer to keep it for when I need it, instead of constantly staying dosed on it and then suffering withdrawal when I go off.

For those who naysay the withdrawal, I've seen multiple people complain of debilitating cluster headaches after about 3 days of no coffee.

The other thing that I've seen is people who complain about anxiety, but start every day with 2 coffees. If you were injecting adrenaline and then complaining about anxiety you would be laughed out of the room, but for some reason with coffee it is acceptable.