Adobe Flash was a fantastic program in the 90s and early 2000s. It empowered users to create fantastic, original content. But like a child who refuses to leave their parents' house, Flash has overstayed its welcome.
Harvey Dent (or Two-Face, if you prefer) would probably say that Flash has "lived long enough to become a villain." Flash is a closed, proprietary system on a platform that was built to be free. In recent years it has been plagued with severe performance issues and major security vulnerabilities.
If you want to improve your privacy and security as you navigate the web, remove Flash now.
Go here to learn more about disabling Flash.
Go here and tell your browser that you don't want to use Flash for YouTube anymore.