It's what cats do. It feels good - they use their claws to stretch their spine and muscles, to exercise, to shed old claw tissues, to sharpen their claws, and, to alleviate boredom. Declawing has horrible consequences for the cat. A declawed cat will frequently bite when faced with even minor threats. Botched surgery can result in the re-growth of deformed claws which curl around under the skin.
Cats lose their ability to balance because they can no longer grasp with their claws.
Other physical problems, such as cystitis or skin disorders, also can be the result of a declawed cat's frustration and stress. With a little effort, you can teach your cat to use a scratching post and leave your furniture alone. Get a tall, sturdy and heavy scratching post. Sprinkle with catnip. Praise your cat when it uses the post.