Why use cider-send-ns-form-to-repl instead of cider-send-function-to-repl in Emacs Cider?

I’m too lazy to go dig into the code now, but it looks like it’s calling in-ns.

(ns toto) ;; never evaluated from the buffer

(defn add [a b]
  (+ a b))
;; => #'toto/add