How does infinite sick leave work?

At one of my previous jobs (in the US) we had unlimited Paid Time Off. In practice, you’re still under the same pressure to get shit done or get canned so you don’t really take any more time off than you would have otherwise. And when you’re eventually canned anyway in order to boost the stock price, you don’t have any accrued time off that has to be paid out in a lump sum.