As the title says. What is the difference between sending response through a channel and just return a map.
(defn handler-one
[request]
(response "hello world")
(defn handler-two
[request]
(with-channel request channel
(send! channel (response "hello world"))
handler-one function uses synchronous approach. Request -> Response
handle-two is a way to achieve Request -> Response but asynchronously.
You can check with-channel macro definition for more implementation details (and documentation).
If you want more details about asynchronous approach in general, then I recommend learning about one of: Futures, Reactive Programming, Netty, Node.js or Vert.x