I don't want to keep quoting Eddie's book, that would be silly, but he explicitly states that one of the biggest problems he encountered when he became England coach is that English players don't go off piste, that they want to be told what to do. This is the opposite of Ozzie rugby players apparently. So in order to get the England players to take the initiative, improvise, play off-the-cuff and problem-solve, he repeatedly puts them in situations that make them uncomfortable so that they have to work things out for themselves. So playing players out of position is part of that drive to make them better at going off-piste. He wants to make them uncomfortable because he thinks it will make them better players.