4Dogs,
As has been the case so often in the past, I think that we generally are in heated agreement.
Certainly, I don't advocate the seat/role swapping other than during the skills acquisition phases of endorsment training for the reasons you list. In the ideal world the training would always be done with an appropriate crew complement especially once one gets to the LOFT components of the program.
However, in the case of same status crew composition, the fact of the matter is that the guy in the "wrong" seat has to be able to perform in that seat's role to a level sufficient not to disadvantage the colleague in the other seat. I am of the view that that entails being able to role play effectively.
In the case of captain/captain, especially on initial upgrades combined with a new Type, the new captain has to have a pretty good knowledge of what his F/O is supposed to be doing if he is to exercise an appropriate level of supervision on the line and, at the end of the day, be able to look after his own interests .. recalling that, at the enquiry, the captain gets shot with a heavy calibre round, while the F/O takes the .22
Except for strict skills exercise repetition, it has been my observation that undue use of reposition is distracting for many pilots, myself included. While the instructor workload increases, I have always found it very satisfying and productive to adopt the flight test philosophy of minimising unproductive time and, for instance, structure tracking and altitude requirements so that one exercise can lead directly into the next with a sensible work flow for the crew and, when it works out nicely, there is very little routine need for freeze and reposition unless the instructor misjudges the gameplan and the crew becomes overloaded.