A higher rate of vacation absence is much less noticeable day to day than a shorter routine schedule in "projecty" occupations where a team effort is pushed to

A higher rate of vacation absence is much less noticeable day to day than a shorter routine schedule in "projecty" occupations where a team effort is pushed to completion. Being on vacation is quite similar to being temporarily assigned to a different project, the temporarily smaller team will cope just fine, they might even win efficiency tho compensate for some of the nominal throughput loss. But most hours reductions are of the predictable continuously reduced schedule type, which is great for occupations where a defined number of positions has to be filled at all times (pretty much everything that is more reactive than active). But in "projecty" work, that predictability is of little value, the reduced-hours teammember will count fully (or more) to team size in terms of organisational overhead and task dependency delays, but will contribute fractionally less. It's not the lower amount of total hours in that scenario, but the permanent asymmetry.