Not as unnecessary as you’d think. Captions exist in part for those without or with poor hearing- to the non hearing who have gained hearing- finding out the sun doesn’t make noise, that wind generally doesn’t make noise nor does falling snow; that gravel or rain make noise or that appliances and things like computer keyboards and noises make constant noise- surprises them. The hearing take for granted that certain things “obviously” make sounds or certain sounds- but for those who don’t have hearing as well as us- knowing what does and doesn’t make what noises isn’t so simple.
Deaf people: *panics*