There are many designs that recommend this. It is a way to mix up the fabrics without cutting out each individual piece. Think of it this way. If you are doing a sauare or other simple shape. If you cut a 4" strip of 6 colors
You stack them on top of each other and sub cut the squares.
then take the top from the second group and put it on the bottom, two from the third group and put them on bottom - etc you will have mixed up all the squares for easier piecing.