There is usually a trade-off in both primary and secondary navigation.
Including more links makes it quicker to get around the site (because there is more likely to be a direct link to the desired location), but clutters the screen and makes it more complicated for users.
In general it is a good idea to keep primary navigation to a minimum because these controls are present on every single page and will clutter the whole site. There is more room for maneuver with secondary navigation (contents pages etc.)
