No need to get out of your car and deal with a dirty pump. You can also get out to go in the store while they fill your tank, or some smaller places you can buy stuff right from the attendant. Gas doesn't cost any extra because of it either. We used to have some of the cheapest gas in the country before a recent tax hike. Basically a free service, no tipping either.

One downside is that if it is busy you might have to wait, but the guys are usually pretty quick.