Many people do not realize that cats also can use scratching as a method of marking, or communicating. Felines actually have sweat glands in their paw pads, and when they scratch against furniture, fences, and other vertical objects, they are actually rubbing their own scent from those glands onto the object to mark their territory. The vertical scratch marks also leave a visible mark for other cats to see as well as smell, and the cat will reach up and scratch downward as an indication of how big he is. Where a cat chooses to scratch is going to be determined in part by whether the cat is a vertical or a horizontal scratcher. Horizontal scratchers will tend to prefer chair cushions, carpets, rugs, and other flat surfaces.
Cats also scratch to groom their claws, and remove old skin and claw sheaths.
Usually, cats who scratch primarily for this reason will scratch in the same spot, vs. cats who scratch in numerous locations, and especially near doors and windows. This latter behavior is much more likely to be that of a feline marking territory. One of the best solutions for cats who scratch in the home is to provide them with a good, sturdy, tall piece of cat furniture, preferably one that provides a variety of vertical scratching surfaces such as carpet, wood and sisal rope. You will want to be sure that the posts of the cat furniture do allow your cat to stretch fully for scratching. You may also want to provide some cat toys with horizontal scratching surfaces.