They're normally required for people who work in a noisy environment.
My other half worked on the ground at Heathrow Airport for many years as an aircraft dispatcher and he was supplied with a stehoscope-like ear defender, only the little rubber cones did not have a hole in them. They protected his eardrums from excessive noise but allowed conversation to be heard from a person nearby. Some units are frequency specific and they do work to protect your hearing in later life. The Health and Safety Executive published this a few years ago:
https://www.hse.gov.uk/research/rrpdf/rr720.pdf
I hope this answers your question.