Blueprint allows you to keep track of the dependencies between specifications. So, for example, if one feature needs to be implemented before another can be implemented, you can record that information in Blueprint. This means that Launchpad can always know which sequence you need to implement your features in.
Use the "Add Dependency" and "Remove Dependency" action links from the menu of the specification to keep track of the dependencies of any given specification. The system will try to prevent circular dependencies (when feature A depends on B which depends on C). In addition, it will in general only allow you to make a feature dependent on another specification in the same product or distribution. In future, we might relax this constraint.