Backing is nothing more than cheap filler, I only use it so I don't have to spend 5-10 more bucks to top off my reel with the good stuff, for filler I used 24lb Chameleon, that stuff is like wire leader even in 8lb (imagine trying to cast wire leader, it's only good for leader :lol: unless your using heavier gear and monster rod guides).
Backing will save you money, since 40lb PowerPro has the diameter of about 8lb Maxima UG, it can go a looooooong ways on a reel that holds 330 yds of 16lb test, I had my reel respooled at Wholesale Sports (old Sportsmans Warehouse) and they put backing and mainline on for me, but I always warn them to be careful with the clickers on the spool since I believe they are at fault for one of mine and my buddies drag clickers breaking.