Shaping baguettes using three folds vs. rolling it up?
One of the key skills in dough making is forming a decent crumb and light texture. While the action of the yeast will go a long way to doing this, by folding the dough in such a way, more air is trapped within the pocket. It is the same way when making pizza, you should not press on the outer crust (or use a roller) on the pie itself, as this expels air or CO2 and could lead to a heavier and less bubbly texture.
While it is not essential, it is generally considered good form to have a light touch when finally shaping bread or pizza. By giving the bread this final forming, the baker is giving their dough every possible chance to achieve decent oven spring when baked.