As Greg described, it saves the Poco one Transformer.
In my areas, I see Open Delta setups for 3 Phase 3 Wire Services, and 3 Phase 4 Wire Services.
The Open Deltas are commonly used where the demand is low (like a peak demand lower than 25 KVA), however I have seen some large 3 Phase, 3 Wire Open Delta setups for Industrial Customers, where the Nominal Demand was in the 100 KVA range.
These setups had Two 167 KVA Pole Mounted Single Phase 120/240V Transformers, spaced on either side of the Pole (similar to Greg's posted Image).
Those setups appeared as if they are anticipating adding a Third Pot later.
There was no indication of an original Closed Delta configuration, where the Center Pot had been removed (due to failure, or another reason).
I will search my Archives for images of those Industrial setups.
Scott
