Mostly, they campaign for things like police accountability and run candidates to force focus on certain issues like surveillance and net neutrality. They don't win, in those cases, but it's a good way to keep solidly-Democratic candidates from letting the issues slide. But there are some Pirates holding offices like town council seats, which is inspiring to me.
(And on a practical level, they seem to be way better at recognizing their position and making an impact than much bigger factions like the Libertarian Party. Perhaps ironically, they've got some great organization.)