One of the cool Site Templates in MOSS is the Site Directory. Using the Site Directory you can categorize your sites, you could for example compare it with the Yellow Pages. In the Yellow Pages you find a SharePoint Consultant by looking first on the category IT.
You can do the same with the Site Directory. You can even add your own categories as well.
By default, selecting a category while you are creating a site is not mandatory, so today I had the question, can we make this a required setting. Yes, is the answer, this is something that you have to enable in the Site Directory settings on Site Collection Level.
On the settings page, you can specify that at least one category needs to be selected before you can create a site.