Not sure what you mean?

You look at the DC gain of the circuit I drew, it will be quite low. The capacitor reduces the emitter reactance, which has the effect of increasing the AC gain. For transistors this is pretty common, they throttle back the possibility of DC changes, but want the best gain they can get for AC, be it audio or RF.

 

Ho Bill, funny how you can view the same thing different ways. I wondered if you were referring to the emitter bypass capacitor, C3.

I don't see this as increasing the ac gain, which open loop hasn't changed, merely removing the feedback provided at DC to stabilise the operating point. Of course with DC emitter feedback the gain is lower at DC.