Wood Screws, as the name implies, are made to fasten woods. The common Wood Screw would have a flat countersunk head to make it flush against the wood surface when fastened.
The regular slot for a Wood Screw is the Philips, star drive or square. Some will also have nibs underneath the head to create a better grip.
Most Wood Screws consist of a smooth shank before the threads begin.
This smooth shank will allow the Wood Screw to focus its grip on the second piece of object and fastens the outermost piece of wood onto the inner one.
Usually, if the Wood Screw was fully threaded, it will not only crack the wood, it will not be able to fasten the woods together tightly. Some will also have the knurled shoulder to give a smoother insert.
Most Wood Screws require a pilot hole before being fastened. Without using a pilot hole, the force of the Wood Screw might crack the wood during drilling.
Also, with a predrilled pilot hole, one can clean out the wood chips in the hole before drilling in the Wood Screw.