In the product info about setting up new workspaces there is a paragraph dedicated to the default workspace and specifically how you must actively restrict access if you don't want all users to have access to it, but no instruction on how to do this. Can you direct me to specific content regarding how to do this?
While these specific Workspaces serve to contain, organize and streamline Users’ Activities on Target - whether it be by region, internal organization, specialty or anything else - Default Workspaces function as a type of catch- all environment, where anyone who has access to Target will have access to that Organization’s Default Workspace. It is up to the Administrator to restrict Users’ access to the Default Workspace and instead assign those Users to the Workspace that specifically concerns their work. For more on Target Workspaces, visit Target’s online community at forums.adobe.com."
First I want to clarify that this part of the KB article you have referenced does not indicate this is a must to do:
"It is up to the Administrator to restrict Users’ access to the Default Product Profile/Workspace and instead assign those Users to the Workspace that specifically concerns their work."
There is no benefit in doing so unless you are assigning Properties to the Product Profile/Workspace and want to make it so that some users only see the activities created in their Product Profile/Workspace and don't have access to the activities created int he Default Product Profile/Workspace it is best to leave the users in the Default Product Profile/Workspace and just managed their access rights from the permissions drop down: Approver, Editor, Observer.
It might not be a good idea to delete the Default Workspace. That is where all of the current activities and users probably live. If you would like to organize I would recommend adding workspaces but there is no real advantage to deleting the Default Workspace.