Google Play Music has been a staple of the Android streaming music scene for a couple of years now, but it's not just good for streaming music off of Google's licensed section. Google Play Music originally made its big debut by letting users upload 20,000 of their own songs to Google's cloud and add them to the library of tracks found within the app. This integrated seamlessly with Google's own streaming licensed music, meaning if you subscribed to All Access you'd not only be getting the 22 million songs that Google currently offers as part of the service, but any of those more obscure albums you might have had in your music collection can easily and freely be added to that library as well.
One of the biggest downsides for music aficionados, however, was that Google used to use a compressed MP3 format for all the songs you uploaded. Now it looks like some users on Reddit have found that when they make their newly uploaded albums available offline on their devices, the file size has significantly increased in the last day or two. Within Google Play Music you are allowed to make any album available offline so that it doesn't have to stream through the network, saving any possible data overages and even helping when you know you're going in an area with less coverage than is desirable.
According to user Tesseract91, many of his albums uploaded before this assumed change were about 1/4 of the size of their lossless versions, bringing the quality of the music down and possibly creating a less than idea user experience. Now when an album is uploaded to Google's servers it looks like it's nearly the same size as its lossless version, giving the possibility that Google is in fact using a lossless format to encode the albums that have been newly uploaded. While the file that's been downloaded is still in an MP3 file format, the actual format doesn't inherently mean that the music is compressed, however to take advantage of this new presumably higher quality format you'll need to delete your uploaded albums and re-upload them to Google's servers.
Google recently updated Google Play Music with some new widgets for mobile, as well as bringing back the device de-authorization limit that was once enforced in regards to how many devices you can use the music streaming service on and how many you can de-authorize.