Dear Jan,
You have already gotten several of the positive aspects of a gas card, and I will add in a negative one...
I myself have never had a gas card, but something I have noticed: Among my friends who do, periodically there is always someone who steals the identity somehow, and starts charging their gas to you illegally.
The gas companies seem VERY good in that they always straighten it out your favor, but there is that inconvenience of going through the process of getting the impinger's charges removed.