There are two parts: contracts and work.
When it comes to contracts, PSPC obviously has a role and a responsibility to assume. It must ensure that procedures are followed and validate the work being done by the other department involved. Sometimes, PSPC must play the devil's advocate. That's what the contractual part is about.
As far as the operational side is concerned, that's up to the departments involved, of course. PSPC is not equipped to handle operations for each of the other departments.