To be most efficient, I think you want to work out the move while pretty fresh, so your technique is crisp and not sloppy. Then you start adding moves into it so you can do the move under more duress while still maintaining perfect form. The key to being able to use the move later is repetition, so it is second nature and your brain is not having to refigure it out.
For these reasons, when I was at my peak of redpointing sport routes I would work them from the top down, figuring out the top moves first and then adding sections further down. This way I had the top dialed in the most, where I would be the most tired. It is obviously the opposite philosophy to onsighting, but the principle of repetition carries over into that style as the body automatically flows into the required movement if you have practiced similar situations.