Hmmmmmm, attacking from two directions or flanking is also sound military strategy. Split attacks were often done during sieges where you have one misdirecting attack to cover the real one.

It's especially useful if you know the besieged enemy on has so many good units to go around. By forcing him to parcel them out you can achieve better results than forcing your way through that single sap point where he can simply keep the bulk of his good forces and bottle you up.