[foz]

The problem with high estimates, if accepted by the stakeholders, is the risk of over-engineering. When given lots of time, development teams often will find ways to use that time which don't add to the value of the features being delivered: over-testing, making things "re-usable", a chance to try something new. And the project is late anyway.

Maybe optimistic estimates are a motivating factor for teams. The desire to finish faster, to be more efficient than you were before, a commitment with a challenge.

In my experience, it takes a strong product owner and a mature development team to meet deadlines. Shipping on-time is always a game of tradeoffs. Accuracy in estimates is usually the result of doing things in a known, measurable way. And by keeping the stakeholders close, you can make critical decisions together to keep a project on track.