Safari takes a page from Chrome with pinned tabs and showing you at a glance which tabs are playing audio. It also borrows a trick from iOS to play nice with Apple TV for YouTube videos and the like.
Safari finally serves up pinned tabs. I have near permanent pinned tabs in Chrome for Gmail and Google Drive and have used them for years. Now, Safari lets you right-click on a tab and choose to pin it to the left side of the browser. Safari still doesn't show favicons on its regular tabs, and it has somewhat of a loose grip on them for pinned tabs. Pinned tabs for Facebook and Twitter show favicons, for example, but other sites including Gmail display a generic icon with the first letter of the site, making it difficult to keep track of which pinned tab is which if you have a large group. Favicon or no, all icons for pinned tabs are gray unless you mouse over it or the tab is your active page.
Chrome shows a speaker icon for any tab that's playing audio, helping you track down a nefarious site that suddenly starts playing a video ad. Safari goes one better by displaying a speaker icon for tabs playing audio and also letting you click on it to mute the tab, saving you from having to open the page to take action. Safari also provides a handy mute-all button in its URL bar next to the refresh arrow.
As you can from an iOS device, you can send a YouTube video to your TV via AirPlay without sharing the whole page. Just click the AirPlay button in the bottom-right corner of the YouTube player.
For more, get all you need to know about OS X El Capitan.