As any regular AP reader will know, YouTube tends to test little server-side changes in its Android app quite often. The latest one we've spotted appears to have been in the pipeline for a while now - a granular mobile data usage setting in place of the standard HD toggle.
left: old. right: new.
The feature's been in testing for a while now; we first received a tip back in March on YouTube 12.07.61. Basically, whenever you're on mobile data, any video you watch will be limited to the quality that you select in the settings. So while you could previously only choose between 480p and no limit at all previously, you can now choose any quality from 144p all the way up to "no quality limit."
For those of you who need to strike the perfect balance between saving data and watching that new video from your favorite YouTube channel, Android Police, this could come in handy. I don't see it on any of my devices; let us know if you are in the comments below.