Before creating a team project, you should carefully plan the scope of the project and consider the future path for the modification, growth, and maintenance of the team project. This topic presents a list of questions you must answer to determine whether you may want to create a new team project or expand an existing project. This list of questions is presented as a starting point for your deliberation and is not intended to be exhaustive or definitive for all software development projects.
This is definitely a good read if you haven't done so already. This document is a sub-topic of Creating and Managing Team Projects within MSDN. So, there is a lot of other useful Team System information at this site.