I had a professor that loved to make simple substitutions to values in questions, where the original question would be incredibly difficult, but if you spotted the substitution, the amount of work you had to do was dramatically reduced. Think something like integrate cos x + i sin x dx, if you spot that cos x + i sin x = e^(ix), and perform substitution, the problem becomes trivial.
Deriving information from facts is a vital skill. But recalling facts is also incredibly important as well. Having knowledge immediately available for use allows a person to apply that knowledge in real-time, which is important for problem solving and thinking on your feet.
