generally for two issues....
1- the edges of most wounds are at highest risk of infection due to debris being caught under the edges of the skin and the hidden spaces of the edges (under skin flap) dry slowest. The center area of the wound is easiest to clean and dries quickly, so lower infection risk there.
2- the ointment can prevent the blu-kot from sticking and other birds will notice the wound quickly, the edges are usually at least partly hidden by surrounding feathers
Also, I usually cut off any feathers within about a quarter inch of the wound edges...they will grow back later but I don't like them tugging on the skin around the edges, when the feather gets tugged it can lift the edge and tear any new scabbing or skin which is starting to heal which again creates an infection risk which could easily be missed on a recheck.