It is not a convention in Clojure. (), [], {}, #{} represent different data structures.

It's really just syntactic sugar, so I would agree with the statement that the convention is being enforced.

You get different data structures. I.e. printing #{ 1 1 2 2 } prints #{ 1 2 } whereas [ 1 1 2 2 ] prints [ 1 1 2 2].

Not exactly, it uses square brackets for vectors sometimes and curly brackets for maps sometimes, yet other times it uses square brackets for maps:

  (let [a 1 b 2] (+ a b))

Instead of:

  (let {a 1 b 2} (+ a b))

(I think my map notation may be wrong, I always just bounce off Clojure so I'm bound to make mistakes).