What is really the purpose of streaming??

I think it is mostly about convenience, but if you use Roon with Tidal it can show you music that you can discover, like, and possibly would have never thought to hear.

There are no sonic differences between cd's and red book 16/44 streams as from Tidal or Qobuz (provided the same DAC is used, of course). The difference is the convenience and the access. The latter in particular is something I value greatly. Suddenly you have access to a very large proportion of all music ever recorded.

Streaming allows you to access more music than you could ever possibly own.  If set up properly, sound quality is not an issue.  There are issues regarding how people can sort through and digest extremely large collections.  Most algorithms are based on "if someone listened to X artist, what else did they listen to".  Most people find that very helpful, but some don't.

Not all "streaming" works the same way.  Spotify (various resolutions, not yet high res, sometimes CD quality) and Tidal (higher resolution, usually CD quality or better, more limited catalog) are subscription "streaming" services.  They do not use physical CDs, of course.

Then there are local hard drive devices (network attached storage) for music storage.  Music files from NAS devices can be played using "streaming" hardware ("streamers").  Again, no physical CD media, but the files are stored locally on the NAS or similar devices.  

The latter approach is the one I use currently, and it allows one to avoid keeping track of physical media (CDs) while accessing all of the stored CD albums via tablet or phone touchscreen app.  VERY convenient, and in my system sounds at least as good as a CD player (i.e., physical media player).

More listening and a vast online catalog of hi res music.

Less time feeding a CD tray like on an assembly line.

CD players are almost all jittery anyway due to the servo motors...