When you draw the bow, you want the forces to be as close to equally distributed through the bow limbs as possible. Using three fingers to draw, whether three under or split, you draw at the balance point to maintain the balance between the limbs. The arrow is further up the string from the balance point when drawing three under than when drawing split.
Drawing split fingered puts the arrow close to the balance point, but not exactly on it. That's why the lower limb is usually a little stiffer than the upper limb, to compensate for the slightly elevated position of the arrow. When you draw three under, the arrow is even higher, which takes the arrow further from the balance point, resulting in more noise and a need for better matching for consistent shooting. I see that as a con, and that's why I stick with split finger shooting.