I will only piece 2 for a quilt if I don't have enough for it.
I had a quilt 100 X 110 and the batting I had was 93 wide, so I cut it off the roll at 110" and added 15" to the 93" to = 115.
When I quilt for others, I give them the left over batting and the trimmings. They paid for it so it is theirs.