"Unlimited Holiday/PTO/Whatever" is a wolf in sheep clothing when you realize the dynamic and psychology of it.

Here is a serie of fun facts about paid time off in many parts of europe, and specifically in France where I'm at, that can help you see the issues :

One, we have a defined number of days, and in fact everytime you see it mentionned it is in weeks. There is no competition, official or unofficial or in you head, or in your manager's head come promotion time about who took more or less.

Two, we have a defined "holiday period" covering several months, where employee are encouraged to take their holiday, and HAVE to take their main holiday (at least 12 continuous working days, so excluding sundays and saturdays), so there is no issue of "it's not the right time" etc etc ... The employer retain a final say in granting holidays and which order people go (to avoid complete service disruption etc ...) but again, any refusal especially in the main holiday period must be justified BY THE EMPLOYER. PS: this is what causes the funny "the whole of France is not working in August" thing.

Three, your days off can only be "pushed back" one year, after that you lose them, so you're very encouraged to take them and not accumulate them years after years, and there is a clear value being shown to you of "you lost X days worth Y €" instead of a vague "you could have".

Four, if you leave the company (either on your own decision or being fired) they need to pay them to you, and it's the biggest expense when ending someone's contract, so employer have a big incentive to keep employee's available day count low, the way to do that being make them go on their holiday.

Five, if the employee doesn't take his holiday during the year, and ends up having a mental breakdown or whatever, it is considered the employer's fault, you are supposed to make sure your employee take their holiday, and yes you can force them to take their holiday in a two year period at the most.

The entire system is built around the knowledge that if you simply say "people can", then you make it a competition between them in front of the boss, so instead we make the ones who don't take holidays a problem.

Now, as a company owner, at first it's scary (oh shit, we're small scale and some employees are going to leave for three weeks, how will the company ever function), but you quickly learn happy people plan to rejoin their job and want it to be not stressfull, so they plan their work in advance, they ask their collegues to handle what calls or emails or whatever need to be done when away, etc ... You essentially never have that issue.

And then you learn the best trick ever to handle stress at work : free, employer sanctionned day off are the employee's equivalent of turning it off and on again. Sometime it's a "you can take a couple day off" and let them decide, sometime it's "you know, take the end of the week ... no it's not a question, don't be there tomorrow" so again force their hand to be off, and you get a much better environnement of work.

Your first impressions as an employer is that holidays are sort of a gift, or a regulation or whatever. If you pay attention, you quickly learn holidays are not a gift, they're a way for your employee to just ... fucking function properly ? Be liberal with it, you don't need to lose sight of work that need to be done, and if you treat your employee as humans you quickly see that they understand that too.

Sorry for the much longer than planned comment.