why make a truck dually? does it do anything important?

Lateral traction for very heavy hauling.

so it does improve traction... thanks :-)

its obviously for the dual dual burnouts!!

It keeps the truck from swaying when hauling heavy loads. It divides the weight between 4 wheels and a wider track.

we used to have a 1994 ford f 350 dually<-sp. It couldnt get traction in snow that was more than an inch deep, it was a long bed, and with no weight in back, its useless in winter, however it was much more stable while towing than reg.

The "more traction" principle will only apply with weight in the bed. With less or no weight in the bed, traction will be adversely affected in anything deeper than 1 to 1 1/2 inches. The primary purpose is to provide lateral stability while towing by spreading the load over a wider contact patch. This same principle will cause the rear end to "float" in soupy or deep conditions with limited weight. The same is true for tractor trailers. Which is why they are much safer to drive when they are fully loaded than when they are empty.