Some companies (especially in the US) have unlimited PTO. I don’t like that. I think the better benefit is a large amount of defined leave. Preferably the company will have a mandatory leave policy.
There is a limit, the company just delegates the definition of that limit to team leads. It makes planning holidays uncomfortable since it’s never quite clear whether you’re pushing a boundary.
Generally I just stick to the UK norm of 25-27 days plus public holidays.
A generous but fixed allowance that you’re actually expected to use in full would be a much better system.
So, "unlimited" PTO is highly subjective. I prefer to be explicit about it and state the exact number of vacation days I am entitled to.
So, when a company says "unlimited," what it tends to mean in reality is "there's a limit, but we won't tell you what it is." This manifests itself in people with unlimited PTO taking (on average) less time off than people with defined number of days.
When you have a defined number of days, you know exactly what the limit is. In my experience, this results in people using most (if not all) of their vacation days.
I will note that this largely seems to be a US thing.