There is another point (not mentioned here) which is applicable in professional services, 'Underpromise and Overdeliver' is not a good approach when you have "super" stars in your team who can overactive the results, but then when a team member needs to be replaced and another one may not keep the bar of that individual.
And what could happen even worse, that overdeliver becomes a new standard.
Therefore, it's much better to master the predictable outcome without any margin on both sides.
There is another point (not mentioned here) which is applicable in professional services, 'Underpromise and Overdeliver' is not a good approach when you have "super" stars in your team who can overactive the results, but then when a team member needs to be replaced and another one may not keep the bar of that individual.
And what could happen even worse, that overdeliver becomes a new standard.
Therefore, it's much better to master the predictable outcome without any margin on both sides.