Make your files smaller by detection and removal of dead code. Dead code means unnecessary, inoperative code that can be removed. Dead code includes functions and sub-programs that are never called, properties that are never read or written, constants and enums that are never referenced.
Dead variables are ones that are never read - even if they've been given a value.
User-defined types can also be dead, and there may be a lot of extra API declarations. Even whole files can sometimes be completely unnecessary. The opposite of dead code is live, operational code. A special case is code that looks live but is still inoperational. This happens when dead procedures call other procedures.