Just my opinion, but I think pulling the trigger and approach go hand and hand. Approach tracks both the situation and the hitter's strengths. Depending on the situation, hitter can isolate his zone, look for his pitch to hit, and swing when he gets it. Until he has two strikes on him. After two strikes, he has to expand the zone, but within reason, to give him the best chance of getting on base and not K looking.
Again, I'm just a dad and never coached above the 12U level, but that's what I've heard hitting coaches teach for years.