I have to say that I'm generally against having any "heavy" pilot involved in normal cockpit operations in two-crew aircraft. Routines are designed for two pilots and quite often the intrusion of a third person can become distracting and sometimes even counter-productive.
Having a "heavy" do the walk-round is certainly OK and can help significantly with getting the show on the road, especially ex-base or after a full shut-down. However, three people on a flight deck designed to be operated by two can at times feel claustrophobic and interfere with the normal flow of events and responsibilities. There is also the view that, if you are used to having a "heavy" always doing some of your normal tasks, the basic two-crew sector will catch you out because the routine of your normal duties has become unfamiliar and un-practised.
Clearly, many situations like diversions, medical emergencies and other abnormals will often benefit from a third person "on task" but in general I believe two-crew aircraft are best operated by two crew. In any event, common-sense dictates that it is essential that the "operating" Captain should always brief on the level of involvement that he requires or expects from any extra crew member(s). Only in extreme situations, therefore, should there be any uninvited intrusion into the basic two-crew flight-deck operation.
JD
