It's made for adjustable gas systems where you can change the amount of gas and thereby the amount of energy that goes back to drive the bcg. The lighter the bcg, the less energy is needed to drive it back, thereby reducing the recoil by lightening the reciprocating mass and the energy needed to drive it. If it was put in a system where the full weight carrier was doing just fine, and not tuned to the new lighter weight, the energy that propelled the full weight carrier back just right would now drive the lighter carrier back with extra energy. That would make it impact the back of the buffer tube with more force and make the felt recoil feel harder.