American cheese is not a flavor. American cheese is a blend of cheese, fat, and emulsifying agents. if there's cheddar in the blend, it'll taste mostly like cheddar, but less of it because it's only, like, half cheddar.

The important part of the American cheese, in figuring out how to use it, is the emulsifiers.

My preferred use case is using a slice of American cheese in mac and cheese, alongside some other cheese (I love Gouda) for flavor. Or like four other cheeses, whatever. Sometimes I mix in a tiny bit of cream cheese or mascarpone or a little milk, which gets emulsified into a sauce thanks to the American cheese, and makes the whole situation creamier. And then I season the whole situation well, especially if I added that last ingredient, to bring out the flavor of the cheeses.

Now, that's not a real, advanced mac and cheese. I could be making a mornay or something. But I'm lazy and I don't really keep butter in the house. So I cheat. Pro chefs might also use other emulsifying agents to control the flavor and chemistry better, rather than just chucking in a slice of some american blend.

but it's a handy shortcut.