Here is the case for playlists (though you guys may not agree):
I listen to a VERY wide variety of music. Like… crazy wide. I listen to IDM, Some EDM, Hip Hop, R&B, Classic Rock, Indie Rock, Indie Pop, Synth Pop, Classic Country, Trip Hop, Glitch, Pop, etc.
About the only think I don’t listen to is Metal.
Now, I don’t think I’m a special snowflake or anything. Most people like a few different types of music. BUT… I’m not always in the mood for ALL of it. If I’m designing… I like something a bit more Ambient. Maybe some Radiohead or Aphex Twin. If I’m prototyping… I like really upbeat energetic music like Flying Lotus. If I’m testing or doing something a bit more boring, I might like a little Patsy Cline. Therefore, it is beneficial for me at least to have playlists.
Notice, I ONLY mentioned things that involve web dev. If I’m having a barbecue or a friend over for beers and ping pong… I’ma need a playlist for that too! What if I want to go running? Now I need some exercise tunes. Good thing Tomahawk works on Android.