[caddemon]

I'm not sure these are good examples, but depressive realism is a pretty legit hypothesis about a potential evolutionary benefit. There's also some hypotheses about energy expenditure - doing nothing is sometimes the right move, although that would have been more important a long time ago than now.

These sort of ideas are hard to evaluate definitively, but I do think it is plausible that mild depression had/to some extent may still have benefits. Of course certain traits can be taken too far though, and when viewed through that lens it is hard to understand how they could be beneficial at all. One could say a similar thing about Autism-like traits.