I'm making a square quilt for our king sized bed. We have a solid brown duvet for our comforter, and I'm not interested in making a full king sized quilt for our bed right now, so the square quilt will go on top of the duvet, on point, mostly to add decorative color to the room, but also for use on my side, as I tend to get cold more than DH.
I also like a square quilt for outdoor or picnic quilts, or if there's a chance I'll be using it as a table topper. Sometimes I just feel like a square format works better artistically too.
RST