Rollup groups and summary accounts

Hi,

Can someone tell what are summary accounts and rollup groups?

I mean what is the relation and difference between them.

Please point to some case study if its avilable.

Thanks
Ashish

Basic Definitions:------------------

Rollup Group -
------------
A collection of parent segment values for a given segment. You
use rollup groups to define summary accounts based on parents in the group.
Define the rollup groups on the Rollup Groups window. Then you assign a rollup
group to a parent segment value on the Segment Values window.
Do not assign a rollup group to a parent unless you intend to use it in a