I don't know how anyone else does it but I make mine with a plastic template. I cut out the shape I want in my case it is for a dresden plate and I find the spot on the fabric I want to use and trace the features on the fabric so I can set it on the next spot in the exact way to get an exact duplicate of the first one. I choose a flower or a line in the design I want to see repeated in my dresden plate. I choose what I want to use.
Stack and whack is pretty much the same idea but you just line up the fabric and cut without much eye to choice. It comes out however it comes out.
Both are good and it is a matter of choice. Stack and whack I have seen are triangles and mine are dresden plates.
Hope that helps.