Why is there a need for project-to-project insulation?

Why is there a need for project-to-project insulation?
What are the indicators that project-to-project insulation is effective?
How does effective project-to-project insulation help all projects deliver on or before the due date, at or below budget, and with the full scope?
List the traditional ways organizations try to insulate projects and why they aren’t as effective as expected.