What is the difference between the Simple Title Case and Intelligent Title Case text reformat options?

Simple Title Case capitalizes the first letter of each word, period. Intelligent Title Case is a bit more selective in what it capitalizes.

For example:
"ceo" would reformat to "Ceo" in simple title case.
It would reformat to "CEO" in intelligent title case.

"director of marketing" would reformat to "Director Of Marketing" in simple title case.
It would reformat to "Director of Marking" in intelligent title case.