What would happen if your current ISP got problems and you had to switch to a different ISP with a new range of addresses (assuming you don't have operator independent addresses and not using BGP)?

I would hope that the firewall guys are using a layer of abstraction in their rules rather than just putting the IPs in each rule individually. Network and protocol objects are fantastic, because you can assign names to network resources and then write rules that refer to hosts and networks by human names.

As an added bonus, if a resource changes addresses you just update the object and all of your rules are updated.