Delta has performed single engine taxi (on twin engine airplanes) for some time now, subject to pilot judgement that it is prudent/safe to do so.

I assume other air carriers utilize this practice also. Given the number of flights at a large airline, it can be a significant fuel saver, to say nothing of the environmental benefits.

With the continually increasing amount of avionics on the airplanes, this procedure does occaisionally cause a delay, because gremlins sometimes rear their ugly heads on “power swap.” This technical problem comes at the worst possible time, when the flight is number 4 or 5 for takeoff.