Topology Manager and the DTAP environment
Because Topology Manager stores information about where to publish in its own database, you can back up a Content Manager database and restore it in another Content Manager environment without taking publishing targets along. In the new environment, you map the same logical publish targets to a new set of physical publish targets.
Most organizations manage multiple distinct Content Manager environments, typically described jointly as DTAP (Development, Testing, Acceptance, Production). Of these, the Acceptance and Production environments each publish to distinct sets of Content Delivery environments. In a typical migration scenario, the Content Manager database in one instance (say, Production) is backed up and restored in another instance (say, Acceptance).
If information about where to publish content were contained in the Content Manager database, then this operation (unless manually remedied) would lead to content from the Acceptance Content Manager being published to the Production Content Delivery environments. That is, content that is not ready to go live would be published to a live Web site.
Instead, this information is in the Topology Manager database, which does not get backed up and restored along with the Content Manager database. Instead, each Content Manager environment has its own Topology Manager instance and Topology Manager database. Content can be moved back and forth freely, while publishing information stays in its place.