Centralizing and sharing your API descriptions, test suites and plans, the various ad-hoc queries people usually keep in their notes or on Slack (and lose), handling involved auth stuff which is a hassle with curl, etc.
I think they gravitate towards the same area as swagger.io or stoplight.io, but from the direction of using the existing APIs.
API schemas and test suites are usually stored as code in some sort of SCM. I googled "postman maven" and "postman gradle" and found nothing official so I guess they have nothing except stand-alone workspaces.
API registry is a useful tool with modern love for nanoservices when a team of five somehow manages ten of those but I don't see anything similar done by Postman. Two of the service registries I know of were implemented in-house for obvious reasons.
