When creating a project, if you do not have the ability to identify named resources to allocate to any part of the project, you can insert placeholders.
For example, you can insert a placeholder called Contractor for part or the entire project. When you have identified the actual resource, you can edit the project and replace the placeholder with the named resource.
A Project Manager who is assigning the roles will keep the extra people in mind without forgetting to add roles at a later stage. This way complete utilization can be achieved with out having to miss out any one from the work force.