This was the transformation that hooked me:

  (transform (subselect ALL :a even?)
    reverse
    [{:a 1} {:a 2 :b 1} {:a 4} {:a 5} {:a 6} {:a 8}])
  ;; => [{:a 1} {:a 8 :b 1} {:a 6} {:a 5} {:a 4} {:a 2}]]

I'm solid with Clojure, and I am not even sure how to begin expressing this transformation without Specter.

Granted, it's not clear why you would want to do this in a real program. But I'm convinced about the generic power of such transformations and have little doubt I'd find use cases (albeit probably not this use case) in real code bases.