If its a round belly bow I'm making, I'll try and round it right with initial shaping of the bow. This way it makes it easier to take off wood for tillering and all that needs to be done is to keep the rounded belly. If you wait till the end to round the belly you'll be lowering the draw weight which, even if it was accounted for, how would you know how much rounding you could do to come in at intended draw weight. Round right from the start.