Subportals are useful if you:
use portals to keep information which should not be visible to subportal users but information in subportals should be visible to portal users.
for example, you run a Payroll Bureau and configure the portals in a way where company directors have access to the portal and employee subportals (where they or you deposit their payslips) and employees see only content in their own subportal.
How to create subportals?
Enter a portal group
Click on "Subportals" and create a Subportal group
Go to a portal of your choice and click on the Subportal group name that appears automatically in the portal navigation tab
Create a subportal for each user and invite them to it