If a recipe is for more than one loaf, or is formed from more than one piece (e.g. a plait) you will need to divide the dough. This is best done with your trusty dough scraper, with the aim of getting it right first time, rather than nibbling bits off one piece to add to the other to even them up.
Ideally, you should check the weight of each piece using electronic scales. Equal weights helps ensure they bake at the same speed, are aesthetically pleasing and, for professional bakers, it is important (or even legally required) that each weighs the same.