If you mean, like, stuff made from fresh ingredients at the grocery store, I'll agree, it's the same stuff that you'd end up making. If it's containerized, there's the whole addition of ingredients for the sake of preservation, and some of that might be worth avoiding.
And so all things equal in the meal, just cost. Buying potato salad is probably more expensive than buying it's parts, although then it's probably not more expensive than starting new versus always having mayo in the fridge, that kinda thing.
I love potatoes but I honestly don't love potato salad.
I flew out of EWR on Friday and my flight left (the gate) on time. Now, we took off 30m late because of the traffic at our final destination, but security was 10m and we were on the plane on time. It was incredible. The longest wait was to get the kids some chicken fingers, that was like 30m.