For years I've been jealous of folks with iOS devices who could just send their phone screens to their Apple TV devices. It seems like the Android screen-mirroring protocols never work right for me. My Sony Xperia has multiple types of screen mirroring, and none of them seem to work on my smart TVs or Roku devices.
YouTube is a completely different story. It doesn't matter if I'm on a laptop, iPhone, Android device or Chromebook, I can "cast" the video to any of my Roku devices or smart TVs without any problems at all. It works and works well. The great part about casting is you can shut off the connection from the sending device, and it keeps playing! Because 95% of the stuff I want to display on the TV from my phone is YouTube videos, I couldn't be happier. Plus, I can check email on my phone while the family watches the latest "Bad Lip Reading" video on the big screen! Take that Apple TV!