Stable amplitude of amplified signal
Just a word of advice about AGC in general.  There is almost always an issue of attack (how fast the AGC reacts to a sudden increase in signal) and release (how fast it reacts to a decrease).  In most AGC cases you will need to make compromises on these two settings to avoid poor behavior from the AGC... it's not a drop-in solution with pre-determined optimum settings for every purpose.  Depending on the program material, you can get obnoxious artifacts like breathing and pumping for speech and music.  ACG is much better at slow drifting things like signal fade.  I just want you know what you might be getting into...