It can also depend on the pattern or lack of pattern that you are making your bargello with. If I were to do Barb's tutorial, I would do it her way because it is all planned out. It is a beautiful quilt and i may do it someday.
On the other hand, sometimes I want to just have fun with a Bargello. I don't know what the pattern will be and it kind of takes on a life of its' own. Not knowing what I will need until I do it, it would not work for me personally to sew that many different strata(as well as having all of those scraps left over).