By default, the Workflow for projects whose Nature is "Product" is the following:
By default, the Default Permissions (Users allowed to read or write the object) and the Default Responsibles (Users responsible for moving an object from one state to another) are set to all users at the Workflow level.
Upon any transition, the user will be prompted to enter comments in a popup. These comments will then be available for review in the Workflow Information dialog box.
Settings
Comments can be disabled by the Administrator by switching off the "Enable Project Workflow Comments" options available in the System Settings workspace, Project Settings folder, Workflow Options tab.