Open delta saves the poco one transformer.
It is really pretty common around here.
This is the typical installation. The 50KVA is the center tapped one and serves the single phase 120/240v loads in addition to the 240v 3p loads. The 25kva is the wild leg (208 to ground) and only serves 3p loads.

[Linked Image from gfretwell.com]

Greg Fretwell