Grass may provide some essential nutrients that are missing from a cat's diet. For example, grass is a good source of fiber.
Eating grass can help to induce vomiting, which can be helpful if a cat has eaten something that it shouldn't have.
Some cats simply enjoy the taste of grass. It may have a slightly sweet or bitter flavor that cats find appealing.
Eating grass may be a natural behavior for cats. In the wild, cats would eat grass to help them to vomit up fur that they had ingested while grooming.
Pica is a condition in which an animal eats non-food items. In some cases, cats with pica may eat grass.
In rare cases, eating grass can be a sign of a medical condition, such as a vitamin deficiency or an intestinal blockage.
If you are going to allow your cat to eat grass, it is important to make sure that the grass is safe.