From my experience, rewatching something is a pretty useful thing for learning English.

It's so because of two main reasons.

First of all, when you watch some movie, tv-series or something like that, you don't even try to understand all speech, you're just watching it. If you understand more than, say, 60-70 percent of all talking, you simply enjoy watching movie and do not strain yourself to understand each and every word. But when you rewatching movie you try to watch it more attentively, 'cause you already know the plot and now try to follow all details which you didn't notice for the first time. So you try to understand more words, truly meaning of the words depending on the context and situations, and so on.

And of course rewatching is one of the best ways to check up your progress in learning English. If you rewatching some movie in a few months' time or even in a year and feel a really big progress in understanding - you are on the right way.

Certainly, it's applies not only to watching something (movies, tv-series, shows, etc.) but also to listening to (audiobooks) and reading.

So, if you don't know what to watch/listen/read next, it's highly recommended to rewatch/relisten/reread something that you watched/listened/read before.