I still remember when being able to sync files with a cloud service such as Dropbox, live, to your Mac or your Windows PC, was a huge deal. Now of course pretty much every cloud storage service has a live-sync app for the Applesoft duopoly, and there are good Linux apps for Google Drive and Dropbox.
They, along with Microsoft's OneDrive, also have third-party-created almost-live sync apps for Android devices, if you've shelled out, as I have, for the models with more storage.
Having more storage means the 1,300-plus tracks I now maintain in my primary listening rotation can all live on both my phone and my tablet without crowding the system files, apps and other user files I keep on them. Using Google's cloud-centered services like Gmail, Docs, and Keep, among others, helps too.
But today I discovered that Google's Play Music app wasn't finding and indexing all of the MP3s I have in my Music folder tree. I tried Amazon's counterpart and found exactly the same problem, leading me to wonder if Amazon merely licensed the guts of Google's app to power theirs. So now I'm using VLC, which also happens to be the standard music player on my Linux Mint laptop. Since it's not wedded to a cloud music stream, it can easily understand and deal with an entirely local music library -- ignoring ring- and notification tones, for example, unlike Play Music.
Yeah. Google's app wouldn't serve up all of my actual music, but it did insist on little now-for-a-word-from-our-sponsor interludes of Carme and Callisto.
Apparently VLC can access streaming services, but I haven't played with that. I don't pay either Google or Amazon to force-stream me music I can't stand, so I wouldn't get but so much out of it. Google won't accept certain tracks I bought with a different Google account, and the utility I used the last time that issue came up isn't available for Linux -- neither is the uploader for Amazon's music storage service -- so even using VLC to stream only my own music library isn't an option.
Yet. Looking back up at the first paragraph, I have to invoke the Y word.