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One or two jobs ago this sort of policy was explained to me as: "If you are getting your work done we don't care how much time you take off. If you are not getting your work done we also don't care how much time you take off"

Combined with perpetual crunch time, it has the potential to be an anti-perk (since then you won't ever get paid for those days).

Nope, you just take as much as you want/need. We dont put restrictions, but expect our team to be respectful and not abuse. As long as you work hard, you can play hard. The type of people we hire understand that and we have never had a problem in the past 2+ years.