In my experience, if you are really prepared for an exam, you know the formulas by heart anyway. I myself passed tests designed in a way that calculators could be disallowed. Some of them even had a reminder section with all the needed formulas. But unprepared students still failed them, because they were simply not used to use them and they therefore ran out of time. This translates in the real world: knowing things by heart and their mechanic is the difference between the guy that spends one hour on a problem ans the guy who spends 10 minutes on it.