I disagree there is at least one purpose I see : they lower the complaint of the neighbors of gun club range. Suppressor can lower the dB enough that good noise isolation can handle the rest.
I would still advise having hearing protection while training though, I learned that the quick way.
Exactly, right on all counts. They also are more pleasant to shoot. The UK has some of the most onerous gun laws of anywhere, yet they don't regulate suppressors. That ought to be a clue that they are essentially harmless.