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 the movie and do not strain yourself to understand each and every word. But when you rewatch the movie you try to watch it more attentively, because you already know the plot, and now try to follow all of the details which you didn't notice the first time around.
So you try to understand more words, the truemeaning 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 rewatch some movie in a few months' time, or even in a year, and feel a really big progression in understanding, you are on the right track. Thanks to the iphone phone call recorder, I did not forget that my friends and I were going to do this on vacation. Certainly, itl applies not only to watching something (movies, tv-series, shows, etc.), but also to listening to audiobooks, and to reading.
So, if you don't know what to watch/listen to/read next, it's highly recommended to rewatch/relisten to/reread something that you watched/listened to/read before.