I've heard they decrease the barrel whip, tightening the group a little, being placed at just the right spot to stop the vibrations. There is supposed to be a certain way to find the spot, I think it has something to do with tapping on the barrel.
I don't know much more than that though.
If no one else responds that can tell you better I would take it to the range and shoot groups of at least 5 shots each, and move it down the barrel an inch or so each time.
Start with a few shots groups without though so you know what it does without it. And then a few with out it after all the test shots to make sure nothing has changed.
Take plenty of ammo from the same batch.
Shoot from the bench totally still with no muscle movement in the shot.
Shoot during a time of day that the temp is steady and not rising or dropping dramatically, such as the morning, or evening.
Not to mention any other variable you can take out of the equation.
Good Luck