This is like Unlimited Webhosting. It is unlimited as long as you are within limits set by board that you cannot know what exactly they are. It is extremely confusing. Better yet - just do 1 week mandatory holiday every 3 months. This way all employees would get fair amount of holidays, they would not take long leaves hurting company workflow and would allow employees to recharge batteries every quarter. Not only you would get rid of people abusing holiday system, but also get workaholics to leave the office for 7 days every 3 months with de-activated entry card so they couldn't just "pop in" for some documents etc. If there is deadline you are worried about - then work late for few days but take freaking holidays. Spend some time with kids. Travel. Sort your issues and re-think your work strategy from safety of house.