I'm still learning Gleam, but I do not believe that "use" has anything to do with async. It seems to be a direct riff on Haskell's "do notation" syntax sugar (<-), which is used for unwrapping monads, but Gleam seems keen on insulating users from these details at the surface level.

The author of the article has an intuition that "use" is helpful for error handling, and it definitely is because one of the core benefits of monads is chaining certain categories with a guarantee that nothing will blow up in the process; however, use cases are broader, as you can chain all sorts of things.

Looking at it now, it's actually akin to clojure's threading operator, which basically just simplifies syntax when making successive function calls (argument threading). Whatever the case, it's not just for errors/async, but more so for chaining without causing a bunch of unnecessary indents to occur.