As others have mentioned the uploaded library feature is NOT quite as reliable as Match. On occasion things show up and disappear...random weird stuff you didn't upload appears in your library, etc. However, it 99% works, and this has the awesome benefit of being FREE. Your whole library, backed up in the cloud, accessible from any Internet capable device.
I love this, because iTunes and iOS have burned me too many times.
Begin rant.
Just recently I lost my entire iTunes library off my main computer. Don't know where it went..just gone. Luckily, it's still on a synced device.
If this was the first backup/sync issued I'd had, it would be one thing, but losing music, photos, backups appears to be amazingly common amongst people I know and going by forum postings.
iTunes and many other big time software like iCloud is NOT always friendly or obvious. People don't know what iCloud backs up as opposed to a local back up, or whether previous backups are overwritten on a sync, or even if you need to sync at all anymore, and then what about wifi sync? How does a company focused on user interface and simplicity continue to screw up this badly with one of their premiere software platforms???
And if you make a mistake and need to retrieve files from a phone or backup, does Apple offer a free product to at least help you out in a bind? Nope, you have to buy some shady forensics software with paypal....
End Rant.
So, yes, access to Google Play Music is a good thing. Also makes it easier to leave Apple's walled garden if you ever decide to migrate away...or even just add a competitors product to your family of devices and want to share (it is your music after all)>