The YouTube Android app is apparently getting a new feature, that has been in testing since around October of last year. And that is autoplaying videos in the home feed of the app. These are muted, so they aren't as disruptive as opening the Facebook app while on a subway. But it is here now. There are settings under the "Autoplay" section which will allow you to turn them off if you wish to do so.
What this feature does is it basically starts automatically playing a video while you are browsing the home feed. It is muted, so it doesn't really do much for you, if you're looking to watch a funny video, or maybe a news clip. Seeing as most of these videos aren't as good without the volume on. Interestingly enough, when you tap on a video to watch, it will continue from where the autoplay left off, and not from the beginning. So in some cases you may need to jump back a few seconds - unless you have skipped past the long intro on some videos. It's not a huge change here, and it's one that most users may not even pick up on right away.
This feature is rolling out via a server-side update, so there's no new update in the Google Play Store for this one. But it appears to be working on all of the devices we have tried it on so far. Google does have a few settings for this feature, which include always on, WiFi only and off. If you are looking to conserve data, you may want to set it to 'off' so that it isn't using more data then you want or need it too. Of course, the 'WiFi only' option would work as well, since most people have much larger data caps on WiFi, if there is one. Just head into the settings of your YouTube app and you should see this new option.