This is sometimes called -- in one of the most Orwellian coinages in the industry -- "unlimited vacation days."
I still agree that it causes ambiguity about how much time off is "too much".
If you're a startup, that can be painful to cough up.
Fast forward to 6 months into the job and I've taken days off for long wedding weekends and have some more extended travel planned in the future.
I agree that "unlimited vacation days" can be a red flag, but it really just means to be more curious and thoughtful about the culture during the interview process and find out what it really means.
Now, some of my coworkers are workaholics and won't take that much. But I have had success in just saying "I want to take these weeks off."