If you have an operation on a single object, you don’t need to define another version just to operate on a collection of those objects.
That is, if you have a function like this:
(defn process-thing [thing] ;; process one thing )
There is no reason to also write this:
(defn process-many-things [things] (map process-thing things))
The idiom “map a function over a collection” is so universal that any Clojure programmer should be able to write it without thinking twice.
Having a separate definition for processing a group of things implies that there is something special about processing a group instead of a single item. (For example, a more efficient batch implementation.) If that’s the case, then by all means write the batch version as well. But if not, then a function like
process-many-things just clutters up your code while providing no benefit.