* No need to have a second device present to stream music. That is, I can start up music with the controller on my phone, and go to the store, but the music still plays since all the streaming is handled by the sonos speaker.
* No need to pair your phone/computer to the device every time you come home. Just get on the wifi, and you're set.
Those are the big ones for me, and honestly they're huge.
On the flip side, the biggest pain point is that you're beholden to whatever music services they include in their controller, and you have to use their controller to play music. So while they support Apple Music, I can't use the Music app on my phone to play it. I have to drill through the Sonos app and find what I want. It works pretty well, but it's annoying. Also, I can't stream Audible books, or Overcast podcasts since they aren't supported by the Sonos controller.