[grandalf]

> allow the previous employee to leave

Ideally the previous employee would feel an obligation (or incentive) to finish as strong as possible, and to help with the recruiting effort for the new hire (and to maximize knowledge transfer).

Mature people understand that sometimes work styles can differ and talented people are not always a good culture fit. So unless the outbound manager is truly immature or unfit to be in the position at all, much is to be gained by being respectful and transparent.