If you ever wanted confirmation of this, suggest to your company that instead of "unlimited vacation", which is really vague and hard to understand, the company give 8 weeks vacation that doesn't accrue or roll over year to year.
Interestingly, that's not legal in California. Vacation is a form of earned income, and must accrue and be paid out at separation. (You can cap accruals, but vacation accrued must be paid, and can't expire.)
There's a legal workaround to that, though: reduce the next year's vacation allotment by the amount of unused vacation the previous year. Raytheon uses this trick to implement their use-it-or-lose-it PTO policy.
Do you think it would survive a legal challenge?
Even if it doesn't, do you have the money to pay the lawyer(s) enough to get it that far? And is it something you care enough about that if you were offered $25k to drop it, you would reject it?
That's what we did, at my partnership. Except that was 1998-2006 and we only provided 5 weeks that don't roll over. I used 4 weeks one year. The rest of the years I barely got over 3. Personal choice though.
It should be noted that unlimited vacation is not expressly legal in CA, it's just never been challenged.