From the “I wish I’d said that” list: Via Frank Patrick’s blog, Mike Cohn, in his User Stories Applied for Agile Software Development. Chapter 10, Why Plans Go Wrong in pdf, explains buffers and padding and scheduling:
“A Buffer Isn’t Padding — A buffer isn’t padding. Padding is extra time added to a schedule that you don’t really think you need but that you add just to feel confident in the estimate. Padding is when I take a conventional approach to building a Gantt chart, come up with three months, but tell my boss four months.”
If you use up your padding, you estimated wrong. If you use up your buffers, unexpected risks popped up. Big difference in what you choose to do.If you (the project staff) mis-estimated, you can use EQF, or other estimation techniques to learn why you mis-estimated. If unexpected risks pop up, you can review them to see if you could have forseen them, or to see if there’s something else you can do to make your project less reactive to risks.