I use Anilist to track my anime and manga. But haven't found anything that provides a similar experience in regular movie and TV show tracking, or even books.
For games, there's a service called Backloggd that uses the IGDb database. For movies, I have used Letterboxd but the Android app is garbage at best.
Oh, ok. Sure... So, I agree that pretty much everything can be done via a browser. But sometimes, the website falls short. The 3rd party clients end up making the service much more usable.
Idk how to explain this better than say, Letterboxd. The app sucks ass. You can't select multiple movies and shows to add to a watchlist or a watched list. You can't perform bulk actions. The UI is terrible. The UX is worse. But if someone were able to make use of the database that letterboxd uses, then that would make my day.