Another thing to keep in mind is that the usefulness of "glue" depends on what it can stick. For example function composition is very useful in functional progr

Another thing to keep in mind is that the usefulness of "glue" depends on what it can stick. For example function composition is very useful in functional programming, precisely because (first-class) functions are used for so many things in FP. Relatedly, "composition" (of functions or anything else) is a powerful idea precisely because the result of a composition is the same kind of thing as the components; hence we can keep composing more and more.