By default YouTube automatically plays videos as soon your they are clicked and this is annoying sometimes specially when you open a lot of pages at one time. There are extensons for disabling video auto play but the problem is they also turns off the pre-buffering of the video which is crucial for slow networks.
You can increase YouTube’s browsing speed by disabling its videos from autoplaying in your Google Chrome web-browser. Stop Autoplay for YouTube is a Google Chrome Extension that stops YouTube video autoplay but allows pre-buffering.