Guess it depends on the manager. AP comes across to me as a very 'hands on' manager, he likes to be there at training and really coaching the squad himself, so perhaps a DoF would be a good addition for him to free up more 'football time' and less time spent worrying about contracts, signings, interviews etc. Other managers tend to take a more back role and let the coaches take training while they tend to oversee the whole package, someone like Redcrap or Wenger perhaps.
Not really got an opinion on it myself, if its what AP wants then go for it, if not, then don't. Simples.