Not all animals drink as much water as they should. Wet foods can be a good source of hydration if your animal is the type that is reluctant to drink adequate amounts of water. And then there are health considerations that can make wet foods a practical choice.
Older animals that have lost some of their olfactory senses may be more inclined to eat a food that has a richer scent and flavor, such as wet foods often are. This is also a good alternative for when a pet is ill and cannot smell as well, or is lacking in appetite. This will assure that they are getting the proteins, vitamins, and minerals they need maintain their health.
Wet foods are a good option as well for dogs and cats with missing teeth, poorly aligned jaws, or smaller mouths.