Al, it would be wrong to say that the high leg serves no purpose. It's useless for line-to-neutral loads.

The high leg is one third of the 3-phase syetem. There are three equal hot lines; the high leg is one of them. It's only "high" because of where, in the triangularly-connected three windings, the grounding wire (a.k.a. the main bonding jumper) is connected.

If it were connecte directly to one of the hot wires instead, then we'd have a corner-grounded Delta. Absolutely nothing is different among the different Delta types (Delta, Corner-grounded Delta, high-leg Delta, etc.) as far as the 3-phase system is concerned.

There is 240v. bewteen any two of the phase wires; 3-phase loads use all three, whether one of them is "high", grounded, etc. Only the voltage between each and earth changes with each method.

Larry Fine
Fine Electric Co.
fineelectricco.com