Imagine you are headed on vacation and planning your driving route on how to get there. What is the first question to answer? The first question isn't where am I going but where am I currently. An effective SharePoint migration requires the same first question, what data do I currently have that needs to be migrated?
Planning out a SharePoint 2010 farm, site collections, user access and many other details need to be done in light of what existing data is being migrated to the new farm. In many ways, it is like the analogy of the square peg and round hole. If we design the 2010 site structure and do not take into account the existing data, it can lead to a difficult transition for both administrator and user.
As the journey to SharePoint 2010 begins for many organizations, take time to map out your 2003/2007 sites. In the process of meeting with site owners, many organizations learn that there are many undocumented sites that have been created over time.
Until we know where we are at, we cannot map out where we are going.