[dreish]

send should never be used in a function that will not keep the CPU busy, such as one that calls Thread/sleep. send-off, which will allocate a new thread rather than taking up a slot in Clojure's fixed-size agent thread pool, should be used instead.

[lukev]

It's fine if you're just using it to simulate a computationally expensive operation, as he is here. In fact, in that case, it's slightly more realistic.