[dmurray]

But in hindsight, it wouldn't be a good comment, because that information is misplaced. The perfect time for you to encounter that comment is the first time you ever encounter the += operator, not every time you encounter it.

I generally think you shouldn't comment to explain your use of a language feature, even an unusual one. The exception: when there exists an idiomatic alternative which you intentionally didn't use, then a comment can explain why.

[IlliOnato]

... or when the feature is counter-intuitive and actively confusing, like "oct" and "hex" operators in Perl that do opposite of what one not familiar with them would guess.

Even after many years of programming in Perl I found comments like

# FROM hex, not TO hex!

useful.