At our first practice, we talked about the importance accurate throws. With younger pitchers, just being able to throw a strike (any kind of a strike) is usually the goal. At the Bronco & Pony levels of play, it becomes important for pitchers to continue to throw strikes. However, pitchers must now start hitting more specific locations within the strike zone.
I usually think of it like this. For Pinto and Mustang, the target is a big rectangle (the strike zone). For Bronco and Pony, the target is now a quadrant within the rectangle--in other words, take the strike zone and place a plus sign within it. A pitcher should be able to hit within at least one of four spots within the strike zone to be effective. At the highest level of play, the strike zone becomes divided into a tic-tac-toe type board. Pitchers with outstanding control (e.g., Greg Maddux) can target a pitch within one of the tic-tac-toe squares inside the strike zone--and he can do it at various speeds!
To be truly effective, a pitcher must be able to mix speeds as well as location. Practicing change-up grips will enable a pitcher to change speeds without making it obvious to the hitter.
Ferguson Jenkins is a Hall of Fame pitcher who was one of the best control pitchers in the history of baseball. In 1971, Fergie pitched over 300 innings, striking out 263 hitters while walking only 37. Nearly all of his 37 walks were either intentional or semi-intentional. In large part, he attributes constantly throwing to a specific target as a reason for his great control. During his off days, he insisted on throwing batting practice to hitters (this is unheard of today!)--so that he could continue to toss baseballs to a very specific target. This is one of the reasons it can be helpful to have our pitchers throw batting practice--rather than the coaches.