In addition to the Issue Type of Change Request the others have mentioned, we also have a step in our Workflow that the Change gets assigned back to the PMO Director for the last step and they go create a new Baseline and make it the default. We have a lot of metrics that track Budgeted vs. Baseline vs. Actual. If the change on the project was material for either Cost, Effort, or Duration, having the new Baseline is important so the project is not "dinged" for having too large a variance between Baseline and Actual. In theory you can run reports against various baselines but we haven't gone that far yet. Also, you can baseline throughout your project life cycle and compare (take one at Kick-off, one once the planning phase is complete, one for every CR or re-forecast, etc.) which we do but again aren't using those metrics yet.