Screws provide a mechanical advantage. Driving in a screw takes less force expended over a greater period of time than driving a nail into the same material. For builders using hand tools, this can make a construction project far easier when screws are involved.
Secondly, what is the advantage of a screw? Screws move objects to a greater depth (or higher elevation) by increasing the force applied to the screw. The mechanical advantage of a screw is always greater than 1 because the output force applied by the screw is greater than the input force applied to the screw.
Accordingly, what are the advantages and disadvantages of using screws?
Screws can rip right through certain materials, making them a poor fastener choice for weak, thin woods. Door skin (1/8-inch plywood) and similar materials may allow screw heads to sink or rip right through. Very soft woods such as balsa will also sink or dent under the pressure of a screw head being driven in.
Is it better to use nails or screws on a deck?
Screws are a "superior" fastener over a nail (they have far superior tensile strength)—especially if you're talking about screwing down decking. Using your deck example—you should use nails to attach the joists to the deck framing but use screws to fasten down the decking itself.