Youtube uses HTML5 now. Why does anyone still have a reason to use flash?
Most functionally useful weather radars, including NOAA's, require Flash. My state's Department of Transportation uses Flash for their traffic cameras. Livestream.com, which hosts my local TV news broadcasts along with other stuff like SpaceX launches, is still Flash. And if I want to view any cable TV programming on the computer, Comcast's player is Flash based.
I'd love to have uninstalled Flash a long time ago; for the time being I have to keep it around and use Flashblock.