Coding Horror has the answer:
http://www.codinghorror.com/blog/archives/001173.html
It's a compatibility feature, allowing older software to run at the speed it was intended to run at (mainly games).
It's a compatibility feature, allowing older software to run at the speed it was intended to run at (mainly games).
I had what, 3-5 PCs with that switch on there, and never once used that feature.