As Davood said, Emitter follower is a circuit with high input impedance and low output impedance. It is used in between gain stages as to isolate the main poles that decide/degrade the bandwidth by the gain stages. As we know that EF has low output impedance, so that this low impedance when parallel with the next stage amplifier which has high input impedance, the total impedance will be even lesser. So, the poles at that point can be moved further up which helps in extending circuit overall bandwidth.
At the same why people say it is reduce feedback, we know that as gain reduce the bandwidth will increase in common circuit, so the effective gain is reduced (a kind of feedback) at the output of the emitter follower.