If the swing draw is done properly one can pull a much heavier bow, not that one should. The swing draw allows a draw that does not require rotation of the torso to begin and then complete the draw, with the straight draw one needs to rotate to reach the string once the bow hand is extended. Also, swing draws reduce the length of rotation of the shoulder joint under the strain of the bow's draw weight. Where I see folks getting messed up on the swing draw is where they begin to pick up draw length. That is they look like they are going to shoot at the ground and then raise the whole works up at three-quarter draw. This tends to get the draw arm elbow high, then to make it harder still they have the tendency to release while the bow is rising with no straight back in the draw.
For some, once they do it right, use it most of the time, others find rotating the torso and shoulders to be easier. For me, with bows that have a higher brace, it is not so important, that inch or two makes a big difference for me, with low wrist longbows I either spread draw or swing draw, making sure the last 6 inches is straight back and the bow is on target and not continuously rising.
"Sheep are a peculiar crowd." -Big Bad Wolf