Your network architecture and your business requirements define the requirements to the type of NAT you require. Going from nat mode to route mode on the interface is painless and easy. As long as you remember, when you change the interface from nat to route you need to nat as part of a policy then.
In my configurations I really never use interface based nat. I like to define it in the policies. My reasoning is that it gives me greater flexibility and control over my internet based traffic. For instance, I may have an application that doesn't work well with port address translation ( hiding an entire network behind a single egress IP address ). I can then define more IPs for that application to use via a policy and a DIP Pool.
But in the end, it depends on your setup. If you have a simple setup, and have just web browsing traffic. Then Nat mode on the interface will work just fine and will provide an easy solution. If you need more granular control. Then set the interface to route mode, and define your NAT requirements in the individual policies then.
Message Edited by shadow on 06-23-2009 11:17 AM