I found this comment enlightening: https://clojuredocs.org/clojure.core/send-off#example-593472...

It seems like there are a lot of parallels between agents and core.async.

Agents, like go blocks, run in a thread pool. Any blocking IO should be pushed off to a separate thread outside of the thread pool. In the case of agents, there is (send-off). In the case of core.async, there is (thread)