IT projects and projects that create new products often are projects with a high degree of uncertainty.
To manage these types of project within a project portfolio is important to set performance targets and metrics by phase (long and short term targets).
The long-term targets are based on the business case and are useful to determine if the project will not deliver the expected benefits.
Whereas, the short-term targets are useful to verify the performance of each phase and to set the objectives for the next one.
Short-term targets are updated at the end of each phase to avoid the risk of measuring the project against an obsolete set of metrics.
Keep in mind: managing projects with a high degree of uncertainty, in a portfolio, requires two set of targets by phase.