If you work in a shelter or bring in new cats, the distemper shot (because it's a combination vaccine) can protect your resident cats from certain respiratory infections.
The rabies shot is important for two reasons.
God forbid, if one of your cats ever gets out, you want that cat to be protected against rabies.
If your unvaccinated cat bites or scratches someone, your local authorities can demand that you quarantine the cat for a certain amount of time, or that you euthanize the cat immediately and have it tested for rabies. (Actually the authorities do that.)
If you don't have the necessary space for a strict quarantine, your local authorities can demand that you hand the cat over to a facility (an animal hospital for instance) for quarantine and you will have to pay a hefty daily fee for keeping the cat at that facility. If you don't want to pay the fee, the cat is euthanized.
By not vaccinating against rabies you are taking terrible, unnecessary chances.
Also, my vet explained to me that rodents can be carriers of the rabies virus, so just simply catching a mouse can put an unvaccinated cat in danger. Bats are another danger because they need such a tiny space to get inside a house. (As tiny as a mouse.)
It can take a very long time for symptoms of rabies to develop, depending on which part of the cat comes into contact with a rabid animal.
The farther it is from the brain, the longer it takes.
I had to quarantine a stray once for six months to save it from immediate euthanasia with no questions asked. Based on everything I learned about rabies at that time, I urge you to keep your cats vaccinated against rabies.
Don't ever allow their boosters to expire.