How often do organizations revisit business case metrics (e.g., NPV, ROI, payback period) during project execution?

Many projects are approved based on a business case containing financial projections and assumptions that may no longer be valid months or years later. Yet, in my experience, once a project is authorized, the focus often shifts to scope, schedule and cost (and risks), while the expected business value receives less scrutiny.

I'm interested in understanding how frequently my peers revisit business case assumptions and what governance mechanisms are used to ensure that projects continue to deliver the value originally envisioned.