Usually I recommend tools that completely replace the YouTube interface, or allow much deeper customization. However, today I'd like to mention SuperYouTube, a Chrome-compatible extension that limits its modifications to very specific points, taking advantage of details like the wide format of current monitors and volume control with the mouse wheel.
Many of YouTube's problems can be summarized as "quality of life". For example, the platform insists on keeping both "Ambient Mode" and autoplay enabled by default. Both functions are annoying for the user and result in a poorer experience, but Mountain View does nothing but ignore the message.
Another negative aspect of its interface is that it doesn't even make intelligent use of available space. If you want to read the video's comments... you have to stop watching it. The same happens with the description, which usually holds very relevant details about the content. The developer of the SuperYouTube extension seems to have recognized these issues, and solves them with tabs.
SuperYouTube: Read Comments and Descriptions Without Stopping the Video
In essence, all that SuperYouTube does is place the comments, description, and recommended videos sections in three exclusive tabs, to the right of the player. To this is added the possibility of controlling the video's volume using the mouse wheel (it's enough to place the cursor over the player for this to work), or deactivating tabs. In other words, if you want the video description to return to the bottom, you just have to deactivate its option.
Not Without Conflicts
Logically, SuperYouTube is not free of conflicts. On one hand, users of theater mode will discover that the new tab section moves down, generating a big void in the interface. And on the other, some users talk about problems with the chat section in live streams... but I think it's an acceptable compromise. YouTube needs a better interface, and SuperYouTube points in the right direction.
Official site and download: Click here