Well you won't really get a more saturated print, that would only be if the person or machine burns the negative for a longer time. That said, by ensuring that the colour layers all receive plenty of light, you are certain of getting the best possible colour print from the film.

You will get a finer grain structure, by over exposing slightly, this works a treat and enables one to get really good definition from a faster film, while still having a slight speed gain from a lower speed film.

Mick.