We call silencers moderators, as they moderate the noise instead of silencing it entirely. You can silence a rifle (or at least .22s) if you have a moderator and sub-sonic loads. There's still a little whoosh of air and a noise from the trigger working.
I've only used moderators on 22lr and .308. On a .308 with normal bullets it makes the noiselevel a lot less irritating. The noise travels a lot less and thus is less likely to disturb nearby animals or people. A 22lr is also much less sharp, meaning I can comfortably shoot a lot without wanting earplugs. I've heard a .243 moderated and that was also a lot less annoying. also .223 for foxes with subsonics and that was very quiet. I was 20 feet away and only heard a click.
Depending where you shoot using moderators can be a requirement.
I bet fosberry knows more, the wierdo. He probably has a moderated .50bmg.