Transformer Turns Ratio 10 vs 30 Excitation

Transformer turns ratio is measured by applying line frequency AC voltage to one winding of a transformer and measuring the induced voltage on the corresponding winding. Historically, most transformer turns ratiometers excite one phase at a time and switch before making a measurement on other phases. This is referred to as switched 1Ø excitation.

The is capable of exciting all three phases at the same time - also known as simultaneous 3Ø excitation. But what are the benefits to this method of excitation?