Look, I didn't do it on the college or pro level (which I think we can all agree is probably much more involved), but breaking down and evaluating film is a very involved process. It's time consuming and it's a huge part of, not only, game planning but also player evaluation, position meetings, practice plan, scout team execution, game preparation, and in-game adjustments. It's clearly something that Edsall is good at and he's someone Caldwell trusts in the position. Although Edsall's not on the sideline, he's a valuable part of the Lions success this season. Is he replaceable? Sure, but at this stage as a head coach, you're not going to hope or trust someone else can fill Edsall's shoes. Is it a glorified position? No, but it's as important as any position on a staff (if not more so). A head coach is only as good as the staff he surrounds himself with. Haven't we learned that yet?
I would also believe that this was discussed with Benedict, agreed upon, and part of his contract.