It would be nice to have a way to restrict the Contacts that can be added to a Smartsheet document to help prevent errors in adding the wrong person (potentially a similar name from a different client). Ideally we would be able to restrict it to the people on the workspace, however that is not supported. The current workaround is to hard code the team member names into the drop down list, rather than pulling from your Global contact list, however that requires more work.