The Project Kaizen folks included boundaries as one of their elements of a successful project. During most of the last 12 months I have worked with three departments of SME on leaning out their websites. If you have ever visited the SME site, you may agree that it could use a lot of improving. One of its navigation problems is that there is just so much information to organize that it is just hard to represent all in one place.
As the project began, it was confined by definition to "content." Another department was actually the owner of the navigation and overall design of the site -- I couldn't infringe on their territory without causing problems. So the content boundary was useful, and could be stretched in a number of ways.
One benefit that I didn't anticipate was the way it eliminated a big source of waste -- the waste of standing around and complaining. Periodically team meetings digressed into criticism and frustration about usability problems in the overall site. The team members were regularly treated to bigtime complaints from customers, so they were sensitized to it. But our boundaries and organizational realities gave us little influence on the overall site's characteristics.
So I had a big stick - our agreement as to boundaries. When talk would head in that direction, I'd just remind people -- sometimes forcefully -- that the global navigation was outside the scope of our project. We wouldn't duplicate its purposes in the hope of giving users workarounds and we wouldn't use up time on pointless discussion. We had ample opportunities within the scope of our project to improve usability, and that's where we would concentrate efforts.
We kept in mind that we couldn't solve all problems in one project, but we would improve what we could. And we did.