[RadioAstronomer]

I personally keep my car above 9/10ths full. You never know when you may need it and cannot get it or don't have the time to get it. So I fill up on the way home every time from work.

Also it is cheaper on the wallet. As the price of gas keeps going up, the stuff in my tank pretty much always cost less that the current prices.

[generally]

I agree about filling the tank being cheaper. The exception is on the rare occasions when gas prices are falling. Then it's cheaper to wait as long as possible. Even then, I keep a reasonable amount in the tank.