I'm not defending this use case, but one example I can think of is that Spotify runs a local server so that websites you access can control it, e.g. if you are on Billboard looking at top music charts, clicking on a song could start the song in Spotify, and even embed a player in the web browser, without you needing to be signed into Spotify in your browser.

Here's an interesting tangential article about how they get around obstacles with SSL certs for localhost: https://letsencrypt.org/docs/certificates-for-localhost/