I have the CC on a lot when I watch TV, but it's not because I'm hard of hearing (although all those years in radio probably didn't do my eardrums any good!) but because I got so used to it when I was caring for my elderly mother, who didn't hear well, that I now can't be without it. 

This article has a bit of irony attached to it - it's from Ireland and some of the UK-made TV shows I watch almost require closed captioning or you can't understand some of the dialogue. The piece even mentions Doctor Who, which I find I can't watch without the subtitles.  

And here's a surprise - according to Netflix, the demo using CC the most turns out to be those aged 18-24, even more than seniors. 

"Looking at why people might choose to use subtitles, 66% of the people surveyed use subtitles to better understand the storyline, while 40% of people said using captions helps them improve their concentration, and this was more common in younger audiences. A Vox poll found a lot of people feel they simply can’t understand what’s being said."

I've noted here before there are other great reasons to use the CC. A song playing in the soundtrack will often be identified in the captions and you won't see that if it's off. And occasionally you'll hear dialogue that's obviously been changed at some point from what it was in the beginning. It's always interesting to see what was altered and wonder why they made that decision.

Bad music mixes sometimes tend to drown out what's being said.

And if you're in a room with other people and there's a lot of noise, it's the easiest way to follow the show. It does take some getting used to, but once you do, you may find you miss it when it's not there. 

Huh? Why We're All Watching TV With Subtitles On