A procured repository is a hosted Repository that procures components from a Proxy Repository while procurement is enabled. For example, one could create a hosted repository named "Approved From Central" and then configure this hosted repository to procure components from the "Central" repository. Once the hosted repository has been created and the source of procurement has been configured, the repository will obtain components from the proxy repository as long as procurement is activated. If you start procurement for a hosted repository, the hosted repository will fetch components from the proxy repository specified in the procurement settings. If you stop procurement for a hosted repository, no additional components will be retrieved from the proxy repository specified in the procurement settings. Without procurement active it is a hosted repository and therefore completely static.
The ability to enable or disable procurement for a hosted repository comes in very handy when you want to "certify" a hosted repository as containing all of the components (no more and no less) required for a production build. You can start procurement, run a build that triggers component procurement, and then stop procurement, knowing that the procured repository now contains all of the components required for building a specific project. Stopping procurement assures you that the contents of the repository will not change if the third-party, external proxied repository does. This is an extra level of assurance that your release components depend on a set of components under your complete control.