[1] Draft can also be referred to as the difference in pressure in the combustion chamber area which results in the motion of the flue gases and the air flow.
For the proper and the optimized heat transfer from the flue gases to the boiler tubes draft holds a relatively high amount of significance.
The stronger movement will also increase the heat transfer rate from the flue gases to the boiler (which improves efficiency and circulation).
[3] Since the stack of a locomotive is too short to provide natural draft, during normal running forced draft is achieved by directing the exhaust steam from the cylinders through a cone ("blast pipe") upwards and into a skirt at the bottom of the stack.
When the locomotive is stationary or in a restricted space "live" steam from the boiler is directed through an annular ring surrounding the blast pipe to produce the same effect.