P3 has a whole lot of stuff happening to it.
Tendons, ligaments, laminae, cartilage, all kinds of good stuff attaches to it.
The shape of the hoof is sometimes referred to as a split cone. The geometry of the split cone is important to how the horse's hoof functions. If you trace the outside of the hoof wall and the front part of P3 you will end up with shapes similar to these.
The lamellar surface area of P3 is about one quarter the surface area of the exterior of the hoof wall. P3 is smaller than most people imagine.
Don't try this at home kids. To trace the front of P3 you have to take it out of the hoof (yuk!). But do try playing around with the split cone. If you make a cone like the one above you can experiment with how the cone bares weight at various angles. You can see how certain angles seem better able to support weight than others. You can also see how too little angle doesn't absorb much shock. Watch how the "heels" move differently at different angles. Sometimes they move outward away from each other, sometimes they move inward and forward. If you play with this long enough you should develop a reasonably good sense for how hoof conformation and trimming effects hoof function (form follows function or function follows form?).