Newton's third law of motion describes the theory behind recoil reducing devices. For each activity there's an opposite and equal reaction. Just said, recoil-reducing devices reduce felt or perceived recoil by redirecting some of the combusting gases on the other side of the projectile to the side instead of adding additional rearward recoil, thus reducing the rearward pulsation or kick.
They additionally help to lessen muzzle lift by reducing recoil and altering gas direction. Every shooter can reap the benefits of recoil minimization, simply because they help remove muzzle rise - which is noticeable when firing in quick sequence whether standing, or sitting. And this is what the AR-15 Muzzle Brake does ? minimize recoil.
People interested in Self Defense, Hunters and Sport Shots need muzzle brakes to lessen recoil to prolong a firing session and to minimize shot to shot times. The objective in all uses would be to stabilize the muzzle for target evaluation/acquisition and or re-engagement.