I make lots of scrappy quilts and I have batted some of them entirely with scraps of batting. I used to carefully zig-zag all the pieces together but now if I know I'm going to be doing pretty dense quilting I don't bother to attach the pieces to each other at all. I just glue-baste them down to the backing, make sure I don't have gaps, trim anything that is overlapping and call it good. Never been able to tell which quilts are batted with scraps and which have whole batting when I'm done. The only evidence is that there's suddenly some space in my batting scrap bin!