1. Zero cost for cat tracking devices, never need to charge them, never need to worry about the cat losing the device.
2. Dramatically reduced chance of your cat being killed by a car. Despite blogs claiming otherwise, I can find no reputable statistics on the number of pets killed by cars in the US, but there are >250k collisions with animals every year. Most are deer, but anecdotally I know many many people who have killed cats accidentally.
3. Dramatically reduced chance of your cat being killed by a coyote or raccoon. Yes, coyotes and raccoons will absolutely fuck up your cat. Yes, they are very likely in your city.
4. Your cat will not be playing a part in the wholesale slaughter of billions of birds, small mammals, reptiles, and other fauna that domesticated cats are responsible for.
5. Significantly longer predicted lifespan for your cat. The life expectancy for an indoor cat is about 14 years. For an outdoor cat, it's 2 to 5 years.
6. Your neighbors will appreciate not stumbling onto your cat's poop while gardening.
Seriously, keep your cat indoors.