RE: What is the purpose of a skeg??
A skeg past the prop on a strut helps with preventing prop walk as the prop goes past half its diameter out of the water.
If the skeg isn't there, as the prop rises out of the water past it's hub it will want to kick out the rear of the boat.
Granted, it is not much surface area, and doubt if it helps a whole bunch, but its there to help. It does'nt hurt anything by being there, in fact it more of a help to have it as it helps protect the propeller against frontal damage. It stays pretty much "transparent" other than that.
It could also be used as a trim tab to take out any prop walk that exists, and leaving the rudder straight as it is.