Logically, if someone is continually using their car on a daily basis they might as well tank up (or nearly so to avoid spillage). Else what's the point in having to go buy petrol more frequently than you have to. It all costs just the same.
There is an argument made (by the super-frugal types) that filling up completely makes the car heavier and drives the MPG down however I see this as off-set against the more frequent trips to the petrol-station if you only half-fill.
