The case that could be made is that the energy, time, and attention of a movement are finite, and those resources can be allocated in a way that makes us /feel/ like change is happening while, in fact, no substantive change is occurring.

It can function like a pressure relief valve. An immediate example that comes to mind is the firing of 6 APD officers that discharged tasers at protestors. Subsequently, nothing structural in the police department changed, but protests dissipated because of the 'victory' and then an even worse botched arrest occured because nothing fundamental had changed.