If you start your site development by planning your site structure, the growth of your SharePoint environment will be logical to your users and administrators. A well-planned hierarchy of sites provides the following advantages:
Security inheritance: Sites that are grouped together so that the subsites can inherit the site groups from the parent sites lessen the time spent on security administration. If you can manage the membership of the site group on one site and then use those site groups on multiple sites, the membership is more likely to be maintained accurately and consistently than if you are maintaining the groups in multiple sites.
Autonomy for teams and divisions: Creating autonomous branches for unique teams and/or divisions allow them to work independently and add content and columns without affecting other teams and divisions.
Logical navigation: The navigation provided with SharePoint 2007 relies to a great degree on breadcrumbs that show you the entire path from your site to the top-level of the portal. By organizing your site structure, this breadcrumb navigation will be more useful to your users.
Aggregation of data: A common requirement for organizations is that content is published in just one location and then displayed in every location pertinent to that content or topic. For example, you can publish a team document that your team members will share, but this content should also be available to be displayed at a division and enterprise ...