I think one thing bad about watching YouTube on Apple TV u will see advertisement and it is quite often. If you directly cast YouTube video to your smart tv using YouTube app or your tv app. Totally no advertisement at all. And Apple TV does not allow adding to queue for YouTube. Meaning one time can only cast one video. Also while you are casting YouTube to your Apple TV, if you are using your phone at the same time, the sound of your games, your apps etc. will be sent to your tv and mix with YouTube video playback for the sound.
It is good if you want to mirror your content to tv from your Apple devices. however, if you purely want to cast YouTube videos to your tv, just cast using the YouTube app ok your phone or your tv app will do.
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