Work item tracking rules is highly customizable. Yet, some rules are not possible with it. One most asked rule is to enforce non-root area path on new workitems to ensure the work items are not lost. Customers can write code to implement those rules, but presently the deployment requires setup on each user's box. Instead, this feature's hope is to read a user defined xml that defines more rules and enforce it in client without needing deployment.
The xml with additional rules could be uploaded in a server location, or even possibly as an attachment to a well known admin workitem. The control will parse the xml to enforce additional rules. Such enforcement will be UI only though, and users could bypass using OM or other apps, and customer would have to enforce UI use by processes.