There's been some discourse recently on project management sites about whether the venerable Triple Constraints are still valid measures for determining project success. Here's a few thoughts:
First, they are not measures for success as much as they are parameters for project planning, scheduling and control. There is still plenty of value in using this model as a way of communicating to project sponsors and stakeholders that the constraints influence project decisionmaking and tradeoffs.
The Triple Constraints do not influence the quality or validity of the project's business case. Nor due they on their own take into account the fact that a project can be late and overbudget and still be perceived as wildly successful.
The triple constraints are just tools. They are valid in helping the PM and sponsor shape basic planning, scheduling and control issues and problems. However, these are not true measures of project success. A project can deliver on all three as well as agreed-to scope (which, by the way, is represented by the size of the triangle - don't tell me otherwise, I will argue with anyone on this forever!), and still be a failure if the business case was not valid or changed mid-project, or if the end users are unable to use the perfectly-executed project deliverables.
New ways of assessing a project add dimension to the evaluation and planning processes. They also, however, raise the debate of the role of the project manager. I do not completely agree with the ongoing movement that posits that PMs should be justifying their projects, making their business cases, etc. That's the sponsor's job - the PM helps. This is where the additional dimensions of project success and evaluation can help all involved to do their jobs more effectively.
