Document Management Community

Hi all,

I am trying to understand the purpose of Communities in Appian's Document Management and its relation to Knowledge Centers.

Are Communities necessary when designing applications? Should an applications' Knowledge Center be placed under a Community? Should it be a top-level object in Appian's Document Management system?

I'm asking all this because there is no option to create a Community from within an application in the Appian Designer in the newer versions of Appian.

A system administrator must go to the Documents tab in the Runtime Data and manually create a Community and only then can a new Knowledge Center be placed under that Community from within the application in Appian Designer.