I have only done praire points one time (so far). Didn't come up with the idea until ready to finish off edges, so had to put them on after quilting, which to me was very nerve-racking because you have to really maneuver the quilt to ensure you don't catch the batting/backing when sewing the prairie points onto top. I vowed then that next time I did them, I would put onto the top before quilting. Of course, the issue of when to put them on likely makes a big difference on whether YOU are quilting by hand or on your domestic machine or if you are sending to long-armer. If you use LA services, make sure you check with them first. Hand-quilting, I would put on before sandwiching. Don't quilt with domestic machine, so perhaps someone who does can give you better advice on which way to do it.
Good luck, you will like the prairie points.