Great question? for simple projects PMs are managing the forecast in PPM. For complex projects they need to keep the official number in PPM but Apptio provide the detail and what if features PMs need.
A complex project is defined as a project that has more than internal labor as part of its resources. Projects that rely on consultant/contractors, and those acquiring software and/or hardware.
One of the data feeds we have from PPM is the labor actuals and forecast (labor and non labor) data, weekly. In this "complex" scenario, PM comes to Apptio sees the actuals and forecast (loaded weekly) edits the forecast as needed, and then the PM takes the Apptio forecast data and updates the data in PPM.
PMs may have reviews of forecast with portfolio managers etc, those are facilitated by the versioning. The TBM office does not get into that part of the process.
Each month when we load actuals from Oracle, we generate a new monthly cycle.
For Quarterly forecasts, once approved (at the portfolio level) we create a baseline version of the plan (From Hyperion) in the planning tool for easy reference by PMs.