Nailing Without Split Ends
Driving a nail near the end of a board can often result in a split. As the nail is driven into the wood it forces the wood fibers apart, causing the grain to split.
An old carpenters trick is to flatten the tip of the nail with a hammer. The flattened tip allows the nail to "chop" through the wood "Crushing" the wood fibers rather than splitting them.
This trick is also useful when installing molding and trim.