On the Nimrod force we flew as constituted crews; the core being the first pilot, first nav, AEO, lead wet and lead dry. That combination was key to maintaining the overall crew operational category. Co-pilot, Nav 2 and the remainder of the wet and dry teams were there to learn and move up through that learning and gaining experience.
Quite frequently you did get temporary changes to the lead positions for whatever reason but the skill of the Ops Flt Cdr was in ensuring the balance and core numbers were maintained appropriate to the operational task.