At HW, with theoretically unlimited vacation, I was only able to take 3 days off per year, first because I was so overloaded with deadlines that I could not identify several consecutive days that I could afford to take off and still meet them, and second, I could not get the days approved by my manager...he always needed me there for something. (I was not in a timesheet role.)
I copied part of someone's post - @1fha+1jfaRTGi - because my experience is almost identical. Due to conflicts with scheduling, I too had very few days of vacation.