I know 1 or 2 people buying cat litter every month and having it delivered, but why? Just go to the store!
Subscribing to deliveries typically gives a discount, which makes the cost cheaper than going to the store and removes wear & tear on your vehicles and your own gas costs.
Depending on what kind of litter you want, the store might not even carry it. My cat litter is from a major brand, but is one that doesn't get as much in stock at my local places and when itis in stock, it's rarely the cheaper, larger box, so that also increases the cost.
Cat litter is fucking heavy. I don't blame anyone wanting it delivered to their door.
The return policy is really what seals it for me. I've never had an issue with returning something, ever.
Other places make it such a hassle and make you pay to return it.