In fact, one of my preferred ways of practicing my knowledge of languages I don't speak very well, is to watch a movie or show in English, for which I don't need subtitles, with subtitles in said language. I've never noticed that it made me fail to notice anything on the screen - it's perfectly possible to watch the show as one normally would AND at the same time try and figure out the subtitles, though of course if you want to understand every word in the subtitles you'll have to hit the pause button rather a lot, since one needs a certain fluency in a language to read and understand subtitles as fast as they appear and disappear.