We used GasBuddy on our trip in both the U.S and Canada. Funny to see people filling up at a station across the street where gas is .30 more per gallon or with GB finding a station just a block around the corner.
It adds up over time. I guess some people buy the higher fuel because they use an oil company credit card or as some people have told me, it's not worth the trouble or "X" company sells better fuel. We filled up with the cheapest fuel. The SUV runs on Mexican fuel 90% of its life and now has 175,000 miles with no issues other than maintenance.
In the case above of DesertCaptain, it was a savings of $5.85. People would drive from one store to another to save that on a purchase of some kind. We traveled 10,000 miles, it adds up. Plus, we slowed down and it saved us an extra 2 miles per gallon which over the trip was an additional average savings of $600.