Sort of like "unlimited vacation" usually means that on average everyone takes less vacation, because they don't want to be the one with the most vacation taken.
If you have defined vacation, the company has to pay you for any unused days when you resign. With "unlimited" vacation they do not. So it's a win-win for the company to offer this supposed perk: peer pressure not to use it, and no financial liability.
If you have defined vacation, the company has to pay you for any unused days when you resign. With "unlimited" vacation they do not. So it's a win-win for the company to offer this supposed perk: peer pressure not to use it, and no financial liability.