The mission is NASA's first demonstration of the agency's planetary-defense initiative to protect Earth from the possibility of a hazardous collision with an asteroid
Dimorphos doesn't pose any threat to Earth, but the DART mission is the first physical test in space of one of NASA's primary tenets: planetary defense.
NASA's Near-Earth Object (NEO) web-site at the Centre for Near Earth Object Studies (CNEOS) reveals that they will be fast approaching the Earth this month