If you have more than just one cat in the home, you may find yourself running into issues with your litter box. Not only are you more likely to have issues with keeping the litter box clean, but you're more likely to end up with issues outside the litter box as well.
Cats prefer their personal space, and if you have multiple cats using a single litter box, you may find them rebelling against you by pooping (or peeing) outside their box, even when it's clean. A simple remedy for this issue? Getting multiple litter boxes, so each cat can stake their own claim to their own private bathroom and you don't have to worry about them leaving deposits elsewhere in the house.
The common rule of thumb is this- for every cat you have, have a litter box available. For 3 or more cats, it's helpful to have an extra litter box, just in case. This is particularly true if you have male and female cats, since they tend to be more territorial than just cats of the same gender.
As always, keep the litter boxes clean and accessible, and always have fresh food and water available for all your pets!