Two of my cats are young and full of bounce, the older female is also healthy so I can't speak from personal experience about the positive benefits of raw feeding for cats with chronic illnesses such a diabetes. However, there are two things I can attest from personal experience: my cats have fabulous coats that smell good, and odor has disappeared from the litter box.
Changes to the Coat
Sassy, a tortoise shell female is about seven years old. She is short haired, but the fur is very thick; it reminds me of the double coat found on a Russian Blue. When she first knocked on my door for a visit, her coat had an oily feel, there were white flakes toward the tail that looked like dandruff, and I noticed a faint unpleasant smell to the fur. About once a week, her previous owner cleaned the fur with a chemical wipe from the pet store.
When Sassy's care transferred to me, I added wheat germ and yeast to the canned cat food, and then gradually added raw meat. If you visited this cat now, you couldn't keep your hands off her. The coat feels like velvet plush, it is never oily, and it always smells fresh.
Alvin and Gouda-Buddha are run of the mill short-haired brown tabbies. When I brought them home from the shelter, they looked scruffy. They were healthy but they were scrawny and their coats felt harsh to touch. Alvin often smelled very bad because he excreted from the anal gland.
Six weeks after I brought them home, I switched them to raw food. "The boys" have muscled up, losing that scrawny look. And both of them have that plush velvet coat, that smells fresh and clean. Alvin always smells good now as the problem with the anal gland secretion cleared up spontaneously.
The Litter Box Effect
Litter box odor is one of the issues that many cat owners contend with. There is a lot of shelf space in pet stores devoted masking or eliminating the smell. My sister is super sensitive to odors. When she visits, she always comments that she can't detect the slightest hint of litter box odor.
To give credit where credit is due, I discovered an absolutely fantastic litter that lives up to its claim of absorbing odor. However, there was a time, when the cats were actually dumping in the box, that an unpleasant smell tinged the air briefly, before they covered up. Even that initial wisp of odor has disappeared since they have been eating raw food.
In summary, if your cat does not have a beautiful coat, or if you are spending a lot of money on products to control the litter box smell, get your cat off food with grain, and onto pure raw protein.