In a word, EVERYONE! Especially in a noisy environment like a sporting event or airport, most people miss all or at least some of the content in announcements and other speech and therefore benefit from captions.
And of course, with a significant loss of hearing acuity, captions become more and more important and audio assistive devices become less and less helpful. At some degree of loss, understanding speech becomes truly “handicapping” or is lost altogether.
How many of us are there? The estimate we use (based upon a 2008 study done at Johns Hopkins University) is that there are 25 million people with a hearing loss that is "handicapping" rather than merely inconvenient; these individuals simply cannot understand speech no matter that the speech is amplified. We refer to ourselves and to people similarly situated as Significantly Hard of Hearing, or SHOH.
Without Captioning, many of these people, including many of our members, respond to this reality by simply staying home. Worse yet, many of us don't stay home alone – our spouses, children, friends and companions often stay home with us. That's not good news for us and it is certainly not good news for public venues. But we will attend if we can understand the performance!
Ultimately everyone benefits from our advocacy but the SHOH cannot do without it.