Large companies, such as retailers with multiple stores will have a manager at each of the stores. The manager of each location needs access to their specific property information and not the others.
Set up the customer or portal to keep anybody from seeing everybody
For multi-location customers, one of two things can work.
Share the email and login with the location # instead of the customer #
Add individual contacts to the customer with unique email addresses and give them access to the portal (bottom check box)