Pieced backs is probably worth a thread of its own! I've done many things with backs, Gemm, and I find the best thing if you can is to deliberately off center when you can so that nobody knows when you are being off-kilter. Notice in my earlier picture of a back made of two very different fabrics, it was all offset. We also typically want to avoid having a seam straight down the middle or in a typical fold location.
While it can be done without quilt as you go, it's pretty darn difficult to stack things solidly/consistently if that is the final result you want -- especially if you want to match a stitch in the ditch on both sides!
When trying to line up a special/fancy/pieced back, I find I typically have to start from the top and slowly, carefully work down to the bottom. Typically I do prefer to work from the middle and then out to the sides, I deal with the wrinkles on the back better that way.
In the attached picture, I made life much harder on myself than it appears by taking a border print and using it for the back of a crib quilt -- there are so many easier ways to do this, like putting the border print down the middle instead of the edges. I like the effect I got but it did definitely add to the complexity of the project!