Vie sans frontieres During flights which have no pax on board, the chances of being crewed with a training captain at the same time are very, very small. We're not allowed to practice emergencies without a trainer and from the client's point of view, they're paying for us to get out and back without undue delay.
Furthermore the passengers offshore waiting for that aircraft to come back offshore again and take them home, wouldn't be thrilled to know that such training is delaying their escape by many minutes or longer. Sometimes the difference between being first down the ILS back to Aberdeen in bad weather, or joining the back of a queue, can be the difference in who calls first on the radio. Similarly who gets the fuel bowser first, back at base and who gets taxi clearance first from Ground Control to avoid delays at the runway holding point. Seconds can count!
Finally I'm not sure of the insurance implications of mixing training into revenue flying, should anything go wrong.