Feather Beta Project is an Opt-in feature fro YouTube which you can join and watch YouTube videos with the lowest latency possible. This is an official beta project by YouTube and they are achieving this by limiting the features available to you in normal mode + also opting for advanced web techniques for reducing bytes downloaded by browser.
Well you might not notice any change on the homepage as it remains the same but when you click on any video to watch it than you can feel a lighter experience. Well earlier sidebar used to contain a bunch of related videos which scrolls deeper and increase the bytes used, well but now after joining the feather beta project you will see only 5 related videos and simple comments nothing else. So all the crap as been taken down and only useful stuff can be seen.
You can join the "Feather" Beta for YouTube and start experiencing a lighter YouTube version. Well do comment below if you feel a major difference after opting for this version.