Success at the gestural (first) stage of the drawing is critical for how the drawing develops in the later stages. This is the point where not only things like rough proportion need to be decided on but it's also where we make the big decisions for the story of the pose. It's much easier to make adjustments at this stage than to try and fix or adjust things down the line. There is a bit of an oxymoron going on here because while we're making all these important decisions that will affect the drawings later development it's also the stage that should feel spontaneous and free, where we bring 'life' to the pose. Good gesture is an art in it's own right and with practice we can learn how to strike that balance.