Cats that regularly eat a small amount of cat grass often have less diarrhea or constipation fewer hairballs and a healthier digestive system overall. You can plant a bit of couch grass too which is supposed to act as a disinfectant for your kittys urinary tract. Cat grass ingestion probably does not have any true benefits for the normal healthy cat other than the distraction argument.
Be sure to remove toxic plants from your garden and avoid using chemicals on your lawn. As a kitten your cat will have got a healthy dose of folic acid from its mothers milk. Even if you cat enjoys eating a lot of wheatgrass in one sitting it is perfectly safe. Similarly the fiber content of grass could work as a digestive aid.