...animating polygon faces...why?
I think the anwser is because it sets keys for all faces you are trying to animate and if you press "S" key then it sets keys for all transferXYZ,rotateXYZ,scaleXYZ and visibility attributes!

Thats about 1000(3+3+3+1)=10000 animation keys!

Try animateing them with deformers or use the channels you only need keys for.

Hope it helps,good luck!