It's not actually unlimited. In fact, by not providing a fixed amount, and calling it unlimited, it lets managers put peer pressure onto people into taking less vacations than if they'd made a fixed amount!
It isn't if they are meek or mid.
In general: it's good to let your employer know that you value your time. If you don't suck, they'll respect you more, not less.
I assume if you took the UK legal minimum of 5.6 weeks for example, you would get fired.