Are grounded outlets important?

The three prong plug was invented in 1928 by Philip F. Labre, while he was going to school at the Milwaukee School of Engineering (MSOE). It is said that his landlady had a cat which would knock over her fan when it came in the window. When she plugged the fan back in, she would get an electric shock. Philip figured out that if the plug was grounded, the electricity would go to earth through the plug rather than his landlady. He applied for and was issued a patent for grounding receptacle and plug on June 5, 1928. As the need for safer installations became apparent, earthed three-contact systems were made mandatory in most industrial countries.