What hysteresis means and why it is needed in receiver AGC?

Could someone please advise what hysteresis means and why it is needed in receiver AGC?

Thanks a lot.

for detail on hysteresis can be found at
http://en.wikipedia.org/wiki/Hysteresis.

how ever in AGC system, (above pic) pin is not contains scale, so I assume some figures.

At pin3 let say the channel faced some more multi path effect or a moving object surround by etc. then pinn will no longer at a steady level and keeps oscillate( up/down around pin3). the system will keep on adjusting the gain controls which is not necessary. so this hysteresis will help the system to relax by this hysteresis and when it cross the limit then it actuate.

in short, it simplifies /smooth the operation of controller.

Specifically, the above is true for signals at the noise threshold (to avoid gain switching due to noise peaks).