There’s a couple of ways to think about it: it gives you a way to talk about List rather than List of T, it enables you to write partial types like partially-applied functions, or it makes it possible to define Monads.
But as I say, none of these things will sound immediately useful unless you have experience of using those concepts already.
I don’t think the benefit ever materializes and highly abstract code is just indulgence.
Much like the people who endlessly tinker with their IDE/emacs/desktop environment/shell in the name of productivity.
People believed (and some still do believe) the same thing about generics.
A real world use-case could be parsing GraphQL raw string queries and automatically infer the returned types based on a common schema, without using special code-generators. For instance you can come up with some magic function `gql_parsed` like:
doc = gql_parsed`query GetUser { user { name }}`
where doc is inferred as something like Doc<Query<{GetUser:{user:{name:string}}}>>
They're fairly common in Scala too, and I believe in OCaml through modules.