Yes it is good to have the binding full. Not because judges want it, but for looks and wear ability. As to size. To achieve a good looking binding there is a relationship between the width you cut the binding and the seam allowance. The wider the seam the wider the binding. Most everyone assums the standard seam is 1/4”. In most cases this works if the binding is cut at about 2 1/4”. If binding is cut at 2 1/2 then the seam may require a little wider, say 3/8”. 3” cut then 1/2”. Etc. this is if you want a good consistently filled binding. Everyone adjusts to what is comfortable and achieves good results. Consistent width of the seam is important. I find that if I don’t maintain good control when sewing the binding the pressure foot will slip and the seam won’t stay consistent. Consistency as you near the corner helps make a good miter as well as the beginning of the next side.