When watching a YouTube video which is embeeded in a webpage, the only problem is you sare stuck with that page. Now if you want to leave that page and open it in new window, you loose all the video buffering. Right ? Wrong if you do it right you will never loose it.
There is a YouTube button, which is like a logo, right next to full screen button at bottom right. If you click on that, the same YouTube video launches in new tab and uses the same buffer, if any, in the new page. This saves loads of time for users who have slow internet.
Below is a video demo : ( Keep an eye on the buffering timeline when I switch to new page )