can someone explain the usecase for this? what kind of apps you'll opens up when you can communicate to apple devices natively? you can't do that before this?

I use it to mount iPhone as a FUSE filesystem in order to download photos using rsync.

Is this also possible with music? Got any links on details about that setup?

Maybe also look into unison ( https://github.com/bcpierce00/unison ) instead of rsync so you get 2-way sync :)