That feeling when you've spent say, 30 days building some feature users asked for, and you finally find a reason to use it yourself, and it works just awesome.
Not the be confused with the much more common one (IME) where it ... doesn't.
@samis git-annex -J flag, for concurrently upload/download with a good progress display.
Currently being used to download a bunch of LCA talks working around my satelite ISP's throttling.
(Rabbit hole to implement it went pretty deep, https://joeyh.name/blog/entry/STM_Region_contents/ )