However, some (all?) states give the employer the right to force you to use them if you build up too many days.
Source: had to deal with a guy on a team I inherited that had built up a bank of 63 weeks (annual plus long service). He did not want to be forced to take them. He politely reminded him that by law they can, so we worked out a payment plan where he took 3 months off a year to catch up. He will celebrate 40 years at the company in a few months.