Project Tolerance is a necessary feature of any project’s plan, as it recognizes allowance of certain variation in duration, budget or quality, to which the project is approved as still successful. It is not exactly a kind of buffer which project managers prepare for smoothing over their mismanagements or inefficiency, but rather it is a tool that we may use to address indispensable healthy variation in results of any project (even with the most accurate estimation). Project tolerance is something that we need to justify for any project model to make it completely robust.
The fact is that we never can predict all possible risks, factors and events waiting for project performers on the way towards their project goals, so we need to envisage a level of project tolerance to which we agree to consider the project as successful and efficient, even though its results (duration, budget or quality) do not meet the preplanned requirements in “exactly-to-a-tee” manner. Determining a project tolerance will help the project stakeholders to avoid a problem of overcontrol and “false alarms” when they try to suit the strict limits of the plan in all-out efforts.