Someone would have to have a disability if they couldn't read subtitles.
But even so, it's more comfortable to watch if you don't have to read dialog. When I watched English shows (which is extremely rare now, thank you very much, Japan :@) I always turned subs on anyways, just for clarity.
Having both the voices, and the subtitles, led to maximum viewing pleasure.
But for Japanese with English subtitles, you get meaning, but you miss out on expression. Of course you can hear if someone is mad, sad, etc, but you can't hear the intonation of a word. If you can, then you probably don't need subtitles.