Cats are natural climbers and the more cat furniture they have to climb, the more content they are likely to be.
Their claws grow continually and they need to scratch to prevent them from growing too long. Without a cat scratching post, this can result in scratch damage to your furniture, walls or curtains.
If you train your cat to use a scratching post, this damage will be substantially reduced, if not eliminated altogether.
It is preferable to have your cat post in position before you bring your cat home for the first time as once they start using a piece of furniture or a wall for scratching, it takes longer to train your cat to use it's cat post.
However, if this is not possible, then be sure to put the cat post as near as possible to wherever your cat is currently scratching.