It support a gigantic amount of website, including audio one. Most of the time, I use it to have an offline copy of a podcast, radio show or some video that I might need to look at wherever I am not guarantee to have an internet connexion (very useful when travelling).
It also has a lot of useful option like downloading the audio only of a video, choosing the quality of the video/audio which might be hidden in the website you are trying to watch it from, download subtitle (this is just so useful), you can pass ffmpeg options also to post-process the video in one go, ... There is just so many thing you can do with it. One last example : one of my computer really struggle to watch video/stream directly from the browser (for whatever reason), but with youtube-dl I can stream directly to VLC/MPV and it use 1/10 the CPU comparing to watching the same video in the browser.
