People spend money on gas, and sometimes one Costco has cheaper gas than another does.
The two Costcos that are nearest to me are listed at $3.65 and $3.79 right now. They're ~25 minutes apart. I think it would be fair to say that there's thousands of people living in-between where the difference in driving distance is irrelevant.
But if they decide that buying gas is a thing they're going to do today, and they can quickly compare the prices beforehand, then: They can use that data to help make an informed decision.
A 14-cent price delta isn't much, but if 11 gallons are purchased then it's enough to cover the price of a Costco hot dog and Coke (with refill). Not bad at all.
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Additionally: While Costco seemingly doesn't make (much) money on gas, that doesn't mean that they're always cheaper.
Suppose I were making a Costco trip today and I also need to buy gas. I'd be heading to the Costco that has gas for $3.65 because that one is much closer for me.
But I can get gas for $3.62 right now at the station down the block from my house. There's no line there (there's never a line there), there's no membership proof to futz around with, and it's super easy to get in and out of.
Since I have enough easy information to make an informed decision, then: I can tell that the smart move is to plan on skipping whatever line may be present at Costco's gas station and just buy gas down the block. This will save me both time and money.
But tomorrow? Who knows. The situation may be different, so I may make a different decision.
Spending any amount of time to save 20.5 cents per day is not worth it to me.
I remember listening to AM talk radio back in the late 90's and a common trope was you'd get someone calling in ranting about gas prices and how they couldn't afford to take their kid on vacation due to current $president in the white house.
Even back in my early teens I'd pencil out the math and it'd be like a $20 price difference for 6 tanks of gas on their 800 mile round trip with the worst fuel efficiency you could imagine. I thought then - as I do now - that if $20 made a difference in you taking a vacation or not you couldn't afford it to begin with.
For most folks it's just an easy topic for people to rant about.
I'd love say that keeping an eye on gas prices and trying to time the market to buy on the right day are things that make poor use of my time. That sounds very nice.
I don't have the financial means to turn a blind eye to these kinds of costs, though. Things are rough over here.
But is that gas station selling Top Tier[1] gas? As far as I'm aware, Costco always sells Top Tier, and now they're rolling out Top Tier+.