It recognizes sit animation inside the object automatically, and turns off your AO sit animation when you sit on it. If no sit animation is set inside, your AO animation will be played as usual. This function is built-in and cannot be turned off.
More details & Get here !!!

*Edelweiss*
http://moekakohime.blogspot.com/
http://slurl.com/secondlife/Zero%20Style/220/71/29
SLX
http://www.slexchange.com/modules.php?name=Marketplace&file=item&ItemID=593983
onrez
http://shop.onrez.com/item/547225