I agree Kelly. I also find it very useful but there is one thing we need to remember when trying to improve language by watching TV.
In order to improve, we need to understand quite a lot. If a programme or a film is too advanced, we will be quickly discouraged and will probably quit. Even if we continue, this will not be very efficient.
The same principle should be applied to using subtitles. If they help us to understand, we should keep them on. However, at some point, when we understand a lot without them, at this point we should stop using them.
To sum this up, I think that watching TV can be a great way to improve the language for intermediate and upper intermediate learners. If somebody is not at this level yet, they may consider watching slow pace YouTube videos in the target language first and then move to watching TV later on.