My kitty had her teeth cleaned last December...5 years old. My vet, who I trust completely and who doesn't do unnecessary things, showed me the tartar on her teeth and said not to wait too long to get it done because it can cause other problems. I had it done the next week. I, too, was nervous about having her put under but she did have to have two teeth removed, and you know, she would probably have had pain eating, etc. at some point if I didn't have it done. When we took her home she was groggy the rest of the day (which was expected) but was absolutely fine the next day.
I am glad we did it to avoid a future medical issue and to avoid tooth pain for my baby.