The only one I've ever done was long ago (the early 70's) to learn different types of pieced block construction...curves, triangles, squares, rectangles, wedges, fans, and combos thereof. Some blocks were 12", some were 6" and it was my own design. Blocks were chosen from a block dictionary. The fabrics were the unifying element.
It was purely a learning tool, the same as a needlepoint sampler, a crewel sampler, or a cross stitch sampler...all of which I did while learning those crafts. I definitely learned a LOT from each of them!