YouTube has recently announced that their web video player will now be defaulted to HTML5 over Adobe Flash. This has benefits to both developers and regular YouTube watchers. One of the reasons they held off on the switch was because back then, HTML5 lacked support for Adaptive Bitrate (ABR) which helped to reduce buffering.
However with ABR support, YouTube claims that they are now able to use MediaSource Extensions to run smooth live streams on a variety of different devices, which includes platforms such as the Xbox One, PlayStation 4, Chromecast, and different browsers such as Chrome, Safari 8, and Internet Explorer 11.
YouTube also points out that because HTML5 supports the VP9 codec, ultimately this could lead to saved bandwidth, load times, and file size, and has encouraged developers to start using the iframe API instead of Flash so that more mobile devices can easily stream YouTube videos. The changes might not be obvious or apparent to the end-user, but if it does what YouTube claims it will, hopefully your YouTube experience down the road will be a smoother and better one.