They quiet the action as mentioned but they also reduce a LOT of vibration, they really make it a smooth rifle to shoot.
The buffer can wear out, but it takes a LONG time. I have a 1022 buffer, that's the actual name of the company, same buffer as the weapon craft just a different color, been using it for a few years, not more than a few thousand rounds, and there is no wear whatsoever.
I believe they are a polyeurothane, there are other buffers that are of different materials, but these are the most popular, not the best, but the most popular.
I have an R/T in my HM2 conversion which is considerably harsher than the 22LR and have about 10K through it, not a bit of wear, just some discoloration from getting very dirty.