With content groups as well as with page parameters, additional information on a page can be stored in Mapp Intelligence.
Content groups are categories and should be used for static information, whereas parameters (as the page parameter) should be used for dynamic information.
A typical use case of content groups is representing the navigation structure of a web site:
Each page is assigned to exactly one element of a content group. For example, en.men.jackets belongs to men in the content group "Page Hierarchy 1", but not to women or another element of this content group. As the assignment of a page to a content group (usually) does not change, this information is a static one.
Page parameters can be used, for example, to track error messages:
As error messages depend on the input of the users, for each page impression it has to be decided whether an error message is passed or not. Therefore, this information is a dynamic one.
By adding the dimension "Pages" you can see how often each page parameter was passed on each page (i.e., which error message occurred how often).
Further information on categories and parameters can be found in the training document Setup Options for the Tracking of Elements.