Every cat needs a litter box. For outdoor cats, that just happens to be anywhere they feel like going, but for indoor cats, litter can make the difference between using the litter box or using your bed, carpet, or kitchen counter instead.
Surprisingly, there are a variety of different litter you can buy. Some are scented, some clump better than others, and some are more environmentally-friendly than others. By simply exploring your options, you can find the best kitty litter for your cat.