Except for case comment and Email message records you can create a field update action that updates a field on the related case record. For e.g. You can create a rule to change the status of a case from " Awaiting Customer Response " to "In Progress" when a customer adds a case comment.

Contact sharing rules do not apply to private contacts. Notes and attachments marked as private via the Private checkbox are accessible only to the owner and administrators. n option on your organization- wide default allows you to ignore the hierarchies when determining access to data. Events marked as private via the Private checkbox are accessible only by the event owner. Managers in the role hierarchy cannot view or edit their subordinate's records if they do not have the "Read" or "Edit" user permissions for the type of record.
Object permissions are set on a user's profile.