Why: because wee can...
probably not very effective but if it's possible why not XD

As far as flash handling multiple cores...
http://Slushnet.dyndns.org

TheS is a 120 fps flash application that uses mathematics to render 3D points into a 2d image.
I've noticed the different speeds on different machines I have tested it on... so one must assume that available cpu and ram affect flash, rendering speed and the like.

I have never tried encoding anything though