Within a single project solution introducing Areas when you have a lot of controllers does improve separation and allows modules to easily be copied in or out of the solution. However in a large enterprise solution I would favour splitting the logic into separate projects instead.
Thus having separate UI, Controller, SOA, Model and Repository projects. In this scenario Areas don't make sense any more, plus they add an extra top level to the Url which is often not needed, although I believe you can omit the area in the Url if you keep your controllers unique, but isn't that a bit smelly?
Perhaps Areas are good for medium complexity sites or when module code is better kept in one location so it can be copied to other sites or removed.