Hearing loss isnt so much an inability to hear "quiet" (despite how hearing tests are performed) as it is a los of dynamic range. By wearing earplugs you can lower the volume of all conversations and prevent "clipping", so to speak.
Try it! Next time you're having trouble hearing someone try to plug your ears with your fingers.
When we'd be out and loud music was playing and somebody couldn't hear what he was saying to them, he'd lean in, speak more softly and place a finger lightly on the front part of their ear (so as to not put his finger in their ear).
He was always much easier to understand one he had done that, and we all picked up the habit. We weren't sure if the finger acted as a conductor, or what the explanation was, but reducing the dynamic range seems like a really good explanation.
They work, but it's annoying wearing them in all the time. I also have Sony XM3 adjusted to reduce most (not full) noise with anc and that helps quite a bit as well.