I'm not sure that you can say definitively that some roles are better filled by consultants, but I would say that some projects are better handled by consultants.
Jesse James GarrettA journalist and an information architect face exactly the same problem - how to give shape to the pile of information in front of you in a way that will make it easy and natural for people to comprehend. I can't imagine any better preparation for the work I do now.
Jesse James GarrettUser-centered design means understanding what your users need, how they think, and how they behave - and incorporating that understanding into every aspect of your process.
Jesse James GarrettIf you need to take a step back from day-to-day operations and plot out the long-term direction of your user experience strategy, consultants can give you a perspective you can't get on your own.
Jesse James Garrett