Universal Apps
Although your smart TV may have every streaming app that you could possibly need, that won’t necessarily be the case for most of your other favourite iPhone and iPad apps.
Since it runs a derivative of iOS, however, you’ll have a much better chance of getting a unified app experience when using an Apple TV. For instance, if you have a favourite weather app on your iPhone or iPad, you may also be able to find a tvOS version of that app to use on the big screen, and of course, all your preferences and settings will sync seamlessly through iCloud.
This also applies to many games — not just Apple Arcade games, but even other iPhone games often have an Apple TV counterpart, allowing you to pick up where you left off in a game between your Apple TV and your iPhone.