I uploaded all of my music to Google Play and deleted it off of my computer. When I get a new computer I only really need my google credentials and then between google drive and google play music I'm up to speed. I install a few packages and I'm at home. I have no need to keep my music there.
Thus there certainly is a reason to do this. Its how photos work on iphones and androids as well. You take pictures, they are put on the cloud, space can be freed up. Its not a malicious workflow
That's not how photos work on any of my Androids. The original files are on the phone, and if I need to make space I can move them to a computer via USB (or dropbox, email, etc.).
You must have the Google photos sync option (or something like that) enabled.
Thus there certainly is a reason to do this. Its how photos work on iphones and androids as well. You take pictures, they are put on the cloud, space can be freed up. Its not a malicious workflow