Ranked in these QuestionsQuestion Ranking
Pro Large catalog of music
Huge variety of music to pick from including rare recordings, covers, mixes, etc.
Pro Community created mixes and remixes
Because anybody can upload to YouTube, it has content from remixes of popular songs to hour long mixes and everything in-between. Much of this content can't be found on other music streaming services.
Pro Really good suggestions
YouTube has some of the best suggestions around. Almost all of the suggestions are similar to the song you're currently playing, and allow for an endless music streaming service.
Con Lots of ads unless you buy a subscription
There are lots of ads on YouTube, even in the middle of long songs. Some of them can be skipped, however others cannot. Most of the time ads are only displayed between songs.
Con Confusing service for music
There is a Youtube Music app, which allows one to stream music videos as well as just the studio audio versions of songs. This feature is not accessible on the Youtube website, or the regular Youtube app.
In order to get ad free service on the site as well as the music app, ones needs to subscribe to Youtube Red for $9.99 a month. This nets the user features, such as Youtube (Google) created movies and videos as well as a way to save musical playlists for offline use, but only in the Youtube Music app. This makes for a confusing and fragmented service that requires using multiple apps, a website, and a subscription to a paid service that encompasses much more than just music, in order to get the full use out of music on Youtube.