Originally posted by sunny
... actually what it do to the ss?
sunny, - like the man said, "If you don't see the difference, leave CalcNormals off."
But for a better answer to your question, a good start would be to read Jim's posts (and others) on this thread.
A mountain of information has been written about this subject over the years,
(much of it by me! 
) - but one favorite of mine is when Mark finally 'Saw the light' -
HERE -