As we've learned from the recipe Creating lists of custom structure, you can create a list of a desired structure and deploy it to multiple sites in your SharePoint solution.
Since lists and libraries are containers of data in SharePoint, business users often require a mechanism to ensure that the correct metadata is associated to list items. In past versions of SharePoint, business users could define whether the metadata field is required to be filled in or not. With SharePoint 2010, you can define custom validation formulas which allow for more granular list item validation.
In this recipe, we'll learn how you can enforce business rules on list items by using list item validation formulas.
The benefit of performing this type of customization using a PowerShell script is that it gives you the ability to apply one or more rules across entire SharePoint farm when required to do so.