The owner of my LBS was fitting a bicycle to a customer. Since he's been doing this for 30+ years, he can usually select the correct frame size for a normally proportioned person by sight. Then he does the standover check and has the person sit on the bike while he holds it to make the initial seat height and for and aft adjustments as well as stem height and such.
Several weeks ago he was doing this for a customer when the customer unexpectedly moved and lost his balance while the owner was checking the plumb line from his knee to the center of the pedal. He grabbed for the owner and fell on him and broke his foot!