Auto-transformers in comparison with the double winding transformers are generally advantageous of the voltage ratio is favorable from the point of view of the equivalent size

The reduction in the equivalent power in relation to the throughput, reduction in the weight and size, reduction in the no load (iron losses) and on load losses (cooper losses), the reduction in the no load current and the short circuit impedance

If P is the power of the transformer, linear dimensions of the auto transformer vary as P0.25 and the weight and volume vary as P0.75 thus reducing the losses and weight of the transformer

The short circuit impedance of the auto-transformer goes down with equivalent rating which is advantageous because of the lower voltage drop and better regulation.

For connections between the two systems at very high voltage, where the power is to be transmitted in the order of GVA (Giga Volt-amperes), the use of auto transformer make it possible for high power equipment and can be easily transportable. This will not be possible with normal transformers