Once you have selected Intercom as your primary data source, all attributes and events displayed in Salesmachine will come from Intercom.
Intercom attributes will be updated in Salesmachine everytime a new session will be made by your users.
When an attribute is updated in Intercom, it will not be pushed from Intercom to Salesmachine until a session is performed on this contact. As soon as the contact performs a session, the entire profile will be updated, attributes included.