...the noise and smell is not for the faint of heart...
Working in a dentist's office, I have seen a wide range of tolerances for discomfort (not pain: we always anesthetize). The people who need ativan or nitrous for a simple filling are probably going to need general for impacted third molars. Those need to be sectioned if they're going to come out without breaking the jaw. In USA, relatively few dentists would offer general anesthesia in a non-hospital setting.
It depends on many factors (teeth being devitalised, expected complications during the surgery, and other non-teeth related factors as well). Some people do get a local anesthesia (not knocked out), others have no choice.
Working in a dentist's office, I have seen a wide range of tolerances for discomfort (not pain: we always anesthetize). The people who need ativan or nitrous for a simple filling are probably going to need general for impacted third molars. Those need to be sectioned if they're going to come out without breaking the jaw. In USA, relatively few dentists would offer general anesthesia in a non-hospital setting.