I can't stand to see people who cut off the edges of the backing and batting and throw it in the garbage can. It makes no sense to me when it is all so useful still and seems rather wasteful. I always ask nicely if I can have the scraps and have only been turned down once (and she dumped in in the garbage can anyway. Ouch!).
I always straighten out the seams and zig-zag them together to make a small quilt batting about the size of a lap quilt. I have never had a problem with the feel of the quilt with these jointed seems.