It's not a decision and choice that any manager should have to make because the decision is hindered by an unreasonable aspect of the game.
As to why it's unreasonable, I think I really explained it.
So, essentially what it comes down to, is that the most amazing possible training minutes imaginable are expected to be delivered when asked. 100% of the time. Signed, sealed, delivered.
The possibility of training 3 players in one position training exists, as does the possibility of training 6 players in two position training, but neither of those things are guaranteed.
In fact, those are sort of the penultimate achievements. So why does everyone keep thinking it's a given? It's the best gosh darn scenario possible. Thus, everyone can't achieve this feat all the time. Certainly, the GE should never be fashioned in a way to arrive at this outcome with ease.