My understanding is that 240 delta with one side center tapped for 120/240 had a limitation that the single phase loads could be no more than 5% to 10% of the total transformer capacity. It's certainly not a choice for buildings that have all or nearly all single phase loads, but so much load that the PoCo puts them in the "must use 3 phase" category.
The 5% loading restriction only exists on center-tapped delta transformers that share a common core. In recent years several manufacturers have starting building some center-tapped single phase units that do not have this 5% restriction.
Transformer banks created by using multiple single phase units may be sized to handle any mix of 3-phase and 1-phase loads.
