Cats need to sharpen their claws frequently during their care, but if they aren't trained to do so in a designated area, they can easily damage furniture. Scratching posts are a great option for cats to sharpen their claws. Don't think that scratching will inconvenience us humans and therefore prevent your cat from doing so; there's a proper way for cats to use scratching posts. 
Cats sharpen their claws to keep them sharp and to mark locations. They sharpen their claws in preparation for hunting. In this respect, cats do retain more of their wild instincts than dogs. Sharpening claws also serves to intimidate others, somewhat similar to the stomping motion of kittens nursing, but the meaning is different.
A cat's forepaws have hidden sweat glands, so when a cat sharpens its claws in its favorite spots, it serves a dual purpose. Of course, cats also mark their territory in other ways. Male cats in heat often urinate in various places, a practice known as spraying. Cats also have sweat glands on the sides of their earlobes, which is why you might see a cat rubbing its head against its owner. The area around a cat's mouth also contains oral glands, so sometimes cats will rub their mouths against their belongings. A cat has a caudal gland at the base of its tail, which is why you often see cats near your legs, wrapping their tails around your calves.
Like dogs, cats use scratching or marking to assert their territory. When a cat is engrossed in scratching or enjoying the process, scolding from its owner is largely ineffective. Therefore, it's crucial to designate scratching areas for the cat as early as possible and provide scratching posts to allow it to vent its frustration. Training should begin in kittenhood to minimize the risk of damaging furniture.
