At my previous company, they specifically created a policy of no more than five days of rollover vacation from year to year specifically because of an on-the-books obligation of a couple million dollars (500+ employees) due to accrued vacation. Later, they changed that policy to NO rollover without VP level approval (e.g. honeymoons). In states like California that have strong employee laws they had to force all California based employees to burn down their accrued vacation every three months. Quasi-ethical and possibly borderline legal but that is what you have to do when employees hoard vacation under the mattress.