The reason for this is the power that each player brings to the table. The first swing high is their ability to hit the ball hard as they walk up the bases. The second swing high is a chance of home run hitting as they reach the plate. Since the second swing high is about 1.15 miles a second slower it takes about 1.15 millionths of a second longer for the pitcher to get a bat out between the first swing high and low. If a ball hits a bat with the last swing high it would bounce off the infield and be dropped to short. Since the second swing high is the last “swing up from a low low” the ball will not have a chance to bounce through the infield with the fastest speed in the game. You can use the second swing high as a “walk to first” if you don’t want to risk the extra throw at the plate. It’s a good reason to use the second swing high in a situation where you already have a batter on if you haven’t already, but you already have two outs. On a play where the bat is up you may want to give it up as there is another batter on so that your team is down 0 and you can “walk to first” in order to catch up and have a chance that you can make it to second and make a play. I know it’s not much of a long shot, but this is definitely a valuable opportunity. If the pitch is high in the zone you can use the second swing high to “walk to third.” In a situation where your team is running out of baserunners and you have to throw, this is a good way to get to third instead of to the second baseman.
The same logic applies to the two ball in play play. It is the most powerful pitch in the game so a pitcher should make the most of the opportunity. If the pitcher has to throw a 3-2 fastball, you can look at putting the bat and ball to the second or third baseman where you can get both of them out with a two ball in play.
How do you handle a hitter in the strike zone? One thing a hitter always does is get on base. This is why swing outs are so important. A hitter can get on base any time they take their base. A batter may get a hit in the first or middle innings of batting practice but that does not mean they are necessarily going to get the hit in the game! The player should always be looking to get on base