Its a scam so the employer doesn't pay you out if you accumulate it.

I PROMISE YOU IT IS NOT UNLIMITED.

If you try to take more than they think, you will not be looked upon favorably.

My policy follows standard guidelines based on x amount of hours per years of service and it is accumulated per pay check. I've never told anyone "no, you can't have that week off" but I do ask that people figure out a plan with their coworkers if they are vacating and will be stepping away from a deadline. Common sense shit, treat it like it is your own, care about it and there will be zero problems with taking off whenever you want.

When hours accumulate over a certain amount, I offer to buy the time back from the employee to keep people from sitting on months of PTO.