I have been doing quite a bit of work with creation\modification rules and I think the following would be useful:-
Rule 1 - City is 'Wakefield' and department is 'Purchasing' = assign value 'member of' purchasing & finance groups
Rule 2 - City is 'Wakefield' and department is 'Accounts Payable' = assign value 'member of' invoicing & finance groups
Rule 3 - Some random rule
Rule 4 - Some random rule
etc
At a future date another requirement is added
Rule 25 - City is Wakefield and department is Purchasing and manager is 'Captain Caveman'= assign value 'member of' purchasing, finance and asset groups.
In this case Rule 25 is the same as Rule 1 with an extra condition, Rule 1 will evaluate to true and then rule 25 will also evaluate to true and take precedence (I hope).
This scenario makes managing rules quite difficult so being able to group or re-order similar rules together would be advantageous.