This feature is only available if enabled through General Settings and if permitted through your login profile. If so, resources that have some interest in the project are listed here. This has no effect on security although a warning will be displayed if a selected resource is associated with an external login.
You can add resources individually or copy them from another project. Click Delete Selected, after checking listed resources, to clear the entries.
Any resources you specify here will have this project listed on their Interested Projects tab. Similarly, if the project is selected there, the resource will be listed here.