A question on party class-mix.

A question on party class-mix. In your experiences as referees and players is it important to have a mix Deft, Strong, Wise and Brave characters? Because of the flexibility of the classes it isn’t as easy for me to see how important the Wizard / Thief / Fighter dynamic is in the game. I see there are new classes out there like the Cunning that blend some of the old classes together. I could just as easily see three Deft characters being successful as a mixed party, or even three Strong characters with the right enemy special abilities. What does your experience bear out?