The restricted who/what list configuration is used for blocking certain types of objects in a CRM from being added to the who and what drop downs in SiX.

When navigating in Salesforce, any object that is clicked on will be sent to the who and what dropdowns.  If you wanted to block all Leads and Contacts from being added, for instance, you can select Prefix and type 00Q,003 in the text field.

If the pattern that needs to be blocked is not at the beginning of the unique id of the object, you must select Contains.