This is confusing to me. How is this better than tests that do the exact same work (document how to use a function, and provide setup to make iterating on a function easy)?
It is advised that once things stabilize you take your learnings and stuff them into a unit test for posterity.
This is just a way to achieve that. However, combined with some of the other clojure niceties (namely cider and structural editing) it does make it a better experience for me.
It allows me to maintain a better flow as I can maintain REPL state if needed(especially if it's a quick hack where dependency injection like component isn't worth the overhead). When I'm done exercising the code I can just make minimal changes to make the comment a test, leave it in place, or move it over to a bag-of-tricks user.clj.
Homoiconicity of Lisp allows you to evaluate any expression or sub-expression without any kind of ceremony. Other languages do not have the luxury of giving you the answer right away. There's always some "ritual" involved, automated or not, but it is still required, but in a Lisp connected to a REPL, you immediately get the answers.