However, feline teeth cleaning is a daily procedure in most practices. There is the usual risks of anesthesia. However, these are not undue, and I think are less than the discomfort, pain and infections that animals with decayed teeth and inflammed gums have. So, yes it is worth putting a cat through the anesthesia. How often to do it seem to depend on the cats.
Biological variability is very evident.
Occasionally there is the 2-3 year old with awful teeth. In general sometime from 4-8 years the teeth seem to have significant buildup of tartar and calculus. I strongly advise getting this done early on. If dental disease goes untouched, the likelihood of extractions or more expensive dental salvage procedures goes up. If your cats have basically sound but need a good cleaning, now is the time.