They are qualified in the eyes of the FAA, but that doesn't make them ready for everything. When someone has to spend 150% of their focus and energy on JUST FLYING the plane, that can lead to problems. We as pilots have to be able to multi task and think outside the box, be ahead of the game, and have a plan b, c, and d. It is very helpful to me as a Captain when my FO can do more than just fly the plane. Why? Because he/she may not have the experience to fly the airplane through the thunderstorms that are unavoidable. He/She may not have the insight or experience with the radar to know which way to go so we don't get the crap kicked out of us. I need them to be able to enter holds into the FMS, calculate bingo fuel, understand why I'm doing what I'm doing and help me keep the lives in our hands safe.