A) I never pay full price for the pre-cuts -- there are good sales out there, and I take advantage of them.
B) You have a huge convenience in getting a wide variety of fabrics that all coordinate, without having to buy yardage of each. So for those of us who can't/won't/don't build stashes, they are a good choice.
C) When you buy small amounts of yardage, you are at the mercy of your cutter. The last 1/3 yard cut I worked with had a significant wave in the cut, and I lost almost 5 inches of usable fabric when I straightened it. The pre-cuts from reputable fabric manufacturers are beautifully straight.
D) Not everyone does well with cutting accurately. If poor cuts lead to bad piecing, frustration, and giving up on a project, which then languishes forever in a closet, you have not saved anything, and you've lost a lot of enjoyment in the hobby.
So precuts may not be for everyone or for every situation. But they are a convenience that makes sense for some people in some situations. I like using them for scrappy quilts w/ a coordinating line. But I can't see myself buying the single fabric jelly rolls-- like a roll of 42 white solid strips, for example. Those I can cut on my own, and pay a lot less doing it.
RST