It is very common for programmers who are new to Lisp to close their parentheses in the former style. However, it is a crutch that they soon do away with if they stick to the language for any length of time.
The first option has both opening and closing brackets on their own lines, while the second has neither. Note that I consider the function name to be part of the opening bracket since it's distinct from the parameters.
which looked really weird to me first but I’ve found it to improve legibility a lot. (Of course there’s a reason it’s idiomatic in Haskell and not elsewhere.)
That the expression is ended I can see in the typical Lisp expression because of the block structure. The single parentheses does make the layout very cluttered and visually ugly. It gets even worse in typically larger Lisp code or data.
Like this:
Instead of