Gee, how did we ever buy cars before Carfax?
Its a false need created by sensationalizing the very small number of "totaled" cars being sold as in perfect shape.
Carfax is like TVfool, only a one-sided approximation. It should still be up to you to figure the rest out.
As to being useful, I jhad one ran (for free by a dealer friend of mine) on a vehicle that I bought and owned for 4 years. It never once saw a garage in 4 years. Carfax showed 8 "instances" on the report!
My mother bought a used Taurus. Totally clean Carfax. After a few months, we noticed air coming in around the rear door seal. While looking for the leak, as we took off moldings, we found putty and air-bag dust. Obviously this car had been in an accident. Where was that info?