[pothole]

I'm the opposite. I rarely fill up even to half way unless I'm just about to embark upon a trip that definitely needs more than half a tank, which isn't often. You don't get a discount for buying in bulk, more gas means more weight and smaller amounts of fresh fuel is better than letting it sit in the tank and go off. It probably doesn't go much, but that's my reasoning.

Of course, the outrageous fuel prices in the UK rather discourage brimming it on a whim, too.