More importantly it forces hitters to speed their barrel up to get to the inside pitch. Once the hitter has sped his barrel up he opens himself up to not being able to stay back on off speed or even a fastball to the outside of the plate. The reason the inside of the plate is neglected is because most youth ball coaches do not understand this and don't want their pitchers to leave a pitch over the plate or hit the batter. Unfortunately most HS coaches I have run across feel the same.
Easy to tell a youth pitcher why we need to own the inside. Quite another for the kid to deploy repeatable mechanics and have confidence in pitch location. The fear factor of one getting away up and in is very real. More so than leaving a pitch middle-middle IMO. The coaches I know are very aware of inside pitching and its value. Its a continual work in progress for the pitcher and coaches.