On the CRM Configuration screen, there is an option to Automatically create Projects for Sales Orders. While this option can be implemented in any xTuple site where projects are used, the feature is really best-suited for job costing scenarios.
When enabled, this feature will create linked projects whenever new sales orders are entered. Since the xTuple job costing functionality revolves around the processing of sales orders, it is helpful to have a project created right at the beginning of the sales order cycle. In this way, the linked project becomes a container for tracking all of a job's costs—from start to finish.