In the seldom cases where your project (or milestone) completion estimation was too pessimistic, do you deliver results right away? If not, which tasks do you assign your team members in the meantime?
From my point of view, there are two contradictory thoughts involved:
+Delivering earlier most likely increases costumer satisfaction.
+Depending on the contract, it may even decrease costumer costs, which even more contributes to costumer satisfaction
-On the other hand, delivering earlier may significantly weaken your position when working with that costumer again ('10 Months? Last time it was a third less anyways, so nevermind').
-It may question your capability to estimate ('This guys estimate was wrong by a third last time either, maybe better find somebody more suitable...').
- Furthermore, even though if it was a fixed contract, you may be in bad position to justify the price. If not, may be even worse, because company management will be unhappy because of lower project value than expected.
Looking forward to hearing your thoughts on that topic.