I am firmly of the opinion that when should be used for side-effects. That's what the implicit do in its body encourages. I think it's an unfortunate coincidence that a single-form `when` is exactly the same, functionally, as a one-armed `if`; once you add more forms the bodies, their behavior is totally different and I find it bizarre that people try to think of them as equivalent. I think you get way more utility out of using `when` as a marker for side effects rather than one-armed `if`s. It should be trivial to examine an if and see if it has both arms, especially with a structurally aware editor. I have never been tripped up by one-armed `if`s, but I have been bitten by unpected side effects. If one-armed `if`s are actually a problem, then I think the solution is to add explicit `nil`s for else arms, not hijack a form with different semantics.

I should add that I'm in the minority here, but I have never heard a good counter-argument from anybody.