Except time.In general, it doesn't cost any more to keep it full than it does to keep it empty.
And except for fuel use. Gasoline can been to go bad in 3 to 6 months, and some folks aren't even using a full tank of gas in 3 months these days. So better to buy a little fresh gasoline than have a tank full of gasoline that could start turning bad. I know my wife's Hybrid actually monitors all that, and runs the gasoline engine to burn off gasoline when it senses the fuel is getting old.Except time.
Filling up once a week vs stopping every day during the week would have very different amounts of time spent by the person doing the filling.