What is the effect of the reflection coefficient?
A reflection coefficient is defined at the junction between two media, usually transmission lines, of different impedance.

At the junction, the power travelling along the first line is split into some power travelling forward into the second line, and some power reflected back along the first.

As such, there is no power dissipation at the line junction. However, the fraction of incident power that gets reflected is no longer available to the second line. It depends on what is driving the first line whether that power eventually gets dissipated or not. A generator with any sort of resistive output impedance will dissipate that power.