This clawing behavior originated in the wild partly for exercise (sink those claws in and PULL!), but mostly to mark terratory. Scent glands in the paws would "mark" the various trees and such in the cat's territory, and by reaching high up on the tree to scratsh they were trying to impress intruders with what a big cat they are. In many ways, they are just transfering this instinct to their indoor terratory.
I have also found that cats have different preferences in the kind of surface they scratch on. With my first two cats, one prefered loop-pile carpeting, the other had a taste for bare wood. I took a clean piece of split fireplace wood and mounted it upright on a sturdy base, then fastened a strip of loop-pile carpet on one side, left bare wood on the second side, and left the bark on the third. Take your pick!. A few cats seem to prefer horizontal scratching to vertical. A cat I had who was like that seemed to enjoy a small braided rug at my parents house. So when my parents passed and we sold the house, I brought the rug home for her to use. Horizontal scratchers who do not seem to care for those coregated cardboard scratchers might like an inexpensive "straw" doormat. Watch to see what sort of surface your cat seems to prefer and give them a similar surface on their post, and you will have better luck getting them to use that and not the furniture.
