My films are close captioned for the hearing impaired. I think that's what you're referring to.
Subtitles are a completely different matter. I subtitle my film if they are not speaking English and it's for b'cast in this country or distributed in English speaking territories. My point about not wanting to put English subtitles on someone already speaking English to begin with is that it is offensive to the person filmed. But sometimes, due to distribution contracts, it has to be done. And if I only choose subjects who are easy to understand (and who will define "easy to understand" to begin with?), then I'm hosed.