Double heading (two locos pulling a train) was used to provide the power to pull heavy loads, climb gradients or meet a tight schedule. With steam trains, each engine was operated individually by its own crew, which took skill, cooperation and concentration to avoid wheel slipping which could stall a train or cause a derailment.

Double heading with diesels is different because all the locos working in multiple are controlled by the driver in the cab of the leading engine.

Double heading is always fun to watch especially on a model train layout, and especially with smoke unit equipped steam locos from yesteryear (enjoy the video!).