If this setting is set to PROPERTY ONLY then rooms in other properties will not be visible to this property.
If this setting allows linking to properties in other accounts, the rooms will be available for linking with the rights set in 'Account Management (in the old control panel SUB ACCOUNT >in the top right) -> MANAGE > ACCOUNT >-> MANAGE PROPERTY >> "Make Property Available in Multiple Accounts".
Click on the 'User' icon on the top right and then on 'Account Management (in the old control panel SUB ACCOUNT in the top right) then MANAGE > ACCOUNT -> MANAGE PROPERTY where "Make Property Available in Multiple Accounts" allows defining the visibility of the property in the control panel, inventory (price and availability) and bookings independently.