I take a "standard" amount of PTO but it still makes sense to have unlimited PTO because:
1. Some people take more and some people take less, and that's fine. Not everyone has the same life circumstances.
2. If you set an allotment, you should track it. Why waste time counting calendar days against a PTO budget if nobody cares? If you start tracking towards a limit that people don't actually care about, then you create opportunities for people to be treated unfairly, or you demonstrate that your organizations rules aren't actually worth following.