I have one in one M14 rifle and not in the other and don't notice any difference between the two. I'll probably put one in the second rifle as I see no liability in it and it does prevent the op rod from striking the receiver.
I've used them in the M1911 but strongly caution against them in that weapon for other than range firing practice. The M1911 design has been diddled with so much that putting a buffer in there will often prevent the ejection of live cartridges in the event of a stoppage -- they shorten the recoil so much the bulltet can't clear the ejection port. And non-standard ejectors make the port even smaller. In this weapon they often disintegrate and can stop the pistol. Even if they work in your pistol on the range remove them before you leave, I've seen way too many problems with them to trust a pistol with one in it.
On my former AK74 the buffer was a literal requirement as the recoil was so violent I'd get a bruised shoulde, something the M1 or M14, or even a 12ga was never able to do.
-- Chuck