When your engine runs it can create very small metal particles caused from metal to metal contact. These particles typically fall to the bottom of the oil pan where they can be picked up by the oil pump/pickup and circulated with the engine oil. This can cause internal engine components to wear much faster, if the metal particle is large enough, it could even cause serious engine damage.
This chrome plated magnetic drain plug from Spectre is designed to hold any metal particles that might fall to the bottom of the oil pan. When the oil is changed, simply clean the magnet off and continue protecting your engine!