Occasionally, it might have a place, but it's everywhere and in quantity. It's a not delicate smear, sandwich shops must be going through 50-gallon barrels of sandwich lubricant. You lift up a sandwich and it squishes between your fingers like a sodden hotel room mattress. I once bit into a cheese baguette and the lubricated filling literally shot out leaving me holding two pieces of damp baguette and a profound sense of disappointment. I'm not joking, the cheese had shot over a fence on a ballistic trajectory from my bready howitzer. It wasn't just a gallon of mayonnaise that hastened its exit, they'd added a tub of chutney to the mix. I was basically trying to eat soup that simply briefly coalesced in a sandwich shaped form like I'd temporarily decohered some sandwich-soup quantum event. Somewhere else, someone was looking at the oozing baguette desperately clasped between their fists and thinking my soup, WHERE IS MY SOUP!
I sort of understand why there's so much of the stuff, in a bout of giddy excitement when I got a new mixer, I made a batch. No human can eat that much mayonnaise. I figure that somewhere there's a mayonnaise national grid and a feed-in tariff. They put a little hole in your kitchen worktop and you scoop it in, and off it goes to be distributed to the nation's sandwich factories or be used as a general lubricant for matters personal or industrial.