Some litter boxes are very large and designed for multi-cat homes. Although many cats are willing to share a litter box, one box is typically enough for a single cat home. Vets recommend you have enough litter boxes for every cat in your home plus an additional box for variety.
If you have a large house, it's wise to put litter boxes in separate locations and train the cats to know where they are. When adding a new litter box, take a small amount of used litter from the old box and put it in the new box so your cats will recognize it.
Owners who take overnight trips should invest in one extra litter box for the cats. While cat-sitters are necessary for trips of two nights or more, an extra litter box and serving of dry food should keep the cats happy during an overnight trip.