In the FCG (trigger and hammer) pins, the "outside" indentations are for the trigger pin and are for the legs of the hammer spring to rest and keep in place. The middle recess in the pin is for the small spring in the hammer to keep the hammer pin in place.
Typically, FCG pins will have one center cut and one outside cut. An illustrative example (I don't know this vendor):
Some people get cute and do a specific trigger pin and specific hammer pin that are not reversible and will walk if you get them backward. Example:
The reason some would complicate the matter is that if you have a gun that's known to be hard on disconnectors and possibly trigger pins like say 416's, MCX's, 9mm AR's...you don't have that weak point in the trigger pin. Unfortunately it's still present and necessary in the hammer pin.