That's why this only works in the right company culture setting. In your case, your employer would have to buy in to the fact that they can't work you like that and expect you to be productive. Eventually, you would just burn out and quit. If your company recognizes that we all need time off to rejuvenate ourselves, they would help you find resources to lighten your workload (or off load) to others so you can take time off.
It's about trust and about a team approach. If you say "I need 2 weeks off at the beginning of December" your team would, ideally, say "ok, we can cover that" and its done. Instead of your boss saying "well, you already used your 2 weeks of PTO this year, so I'm sorry it's not possible."
I've worked for 3 companies now and I've never had anyone ever say "no" to a PTO request. So, if they never say no, what's the point of having a policy in the first place?