Disclaimer: I live in Germany, where laws are a bit different from the US. For example, sick days - even when you get sick during your vacation - don't count towards your regular paid time off bucket. I think the principles that I'll describe still should hold true, though.
What traditional vacation policies really do is define a paid time off budget. Someone, sometime figured out what he thought was a "fair" amount of time per year, and that's what you get. Maybe even a little more, depending on your employer and negotiation skills.
Makes sense? Well, let's do a thought experiment: imagine being self-employed. Imagine that someone - maybe the government - tells you that you should take exactly x days of vacation a year. Still makes sense?
If you are anything like me, you would resist that dictate. You would want to take responsibility for finding the right balance between financial, mental and physical health - of both yourself and your family. Instead of figuring out the right balance once and for all, you would continuously adjust your plans - to your own needs, those of your family and customers, and to the development of the market.
So why does that stop once we get employed by a company?
I think it shouldn't.
Of course, once you have colleagues and stakeholders, the whole situation becomes even more complex. A fixed time vacation policy reduces that complexity. But it also takes away your responsibility to make decisions that make sense. And that's not a good thing, in my opinion.
What would be needed for a vacation policy to work that doesn't work with a budget? In short, every employee needed to be an entrepreneur who feels equally responsible for himself and his family, his colleagues and the organization. That includes, but is not limited to (pun not intended):
- every employee having a good understanding of his own needs, the needs of his colleagues and the organization (and being in a constant dialog about it),
- feeling responsible for creating a good balance between those needs, in cooperation with his coworkers; as a consequence
- a culture where coworkers hold each other accountable - not only for work results, but also for taking care of themselves, and
- a culture where the inevitable conflicts are dealt with productively.
So, it's not about removing the limit, letting every employee have "as much vacation is you want", inside a traditional culture of "getting away with as much as I can". It's about creating a culture of "we are in this together", where - as a consequence - such a limit wouldn't make sense.
PS: if your vacation needs to be approved by a manager, you probably don't have unlimited vacation - you have a variable limit that depends on the whim of your manager.