i'm another who will not go back to previous methods of basting, now that I have discovered 505 spray. I love the speed with which i can baste a quilt using 505 and I love how neatly my backing stays while I am machine quilting. I never have to worry about puckers using the method I described previously.
There are all kinds of basting sprays out there, for all kinds of crafting. So it is not a good idea to lump them all together. 505 is great for basting quilts and it has no odor to speak of. (I am very sensitive, have to have windows open when painting, etc, and i have no problems with it, however everyone needs to take into consideration their unique sensitivities and philosophies).
You can totally avoid overspray by spraying from the edge of the quilt toward the center of the quilt and go no further than the edge on each end. if you are concerned, put a sheet down on the floor when you spray a large quilt or place paper down beside a wall quilt. Just avoid trying to spray an entire quilt from one standing position. You have to move around the quilt as you spray and you should not have a problem.
Lisa