Several customers use the Contract Request for the entire front end for procurement. Since all team members can use the contract request functionality, this is where project go-no go decisions/approvals are made. I have 1 customer who uses the contract request to cycle the contract information through budgeting, the CIO plus all of the delegation of authority approvers. The final routing is to procurement who then create the contract workspace.
Another use case is for the contract request user to request procurement services and, based on the expected amount of the purchase, whether there is a preferred supplier already under a master contract and other factors, the request may be routed through sourcing for a sourcing project (RFP, quick project, etc.) or it may simply go straight to contracting.
To Mark's question, in the Contract Request template, on the Documents tab, you can place 1 or more sub-projects which can be your sourcing or contracts templates that you'll use. These can be condtioned so that they only appear after approval and only can be created by a user with proper permission.