I make a lot of Project Linus quilts, so the 60" wide on a roll is perfect for that. My Hobbs 80/20 batting is 90" wide and comes on a BIG roll, which I keep standing on end in the corner of the guest room. When guests come it goes into the unused shower in the extra bathroom. I do get individual batts at estate sales. After cutting into them, I put them back into the same bag and mark the measurements on the bag.
As for leftover batting -- the fluffy batting is used by charities that make stuffed teddy bears. The cotton batting pieces I save for QAYG, as well as the long edge pieces (for QAYG borders). Little pieces are great to put near your sewing machine at sew-ins for the purpose of catching threads -- just put in the trash when you are packing up.
Also, I use odd pieces of fluffy batting for packing when shipping. The fact that they are lightweight makes them ideal.