I’ve been asked why we separated business rules from requirements in Contour. When we designed the application we decided to keep rules separated so they could be reused and linked to multiple requirements. I decided to do a little research to see if that makes sense.
Ellen Gottesdiener of ebg consulting has written a number of articles on requirements including several on business rules. She makes the case that separating out rules is a best practice. Though several years old, I think the articles on business rules are applicable today.