A drogue parachute is more elongated and has a far smaller area than a conventional parachute and therefore provides less drag. This means that a drogue parachute cannot slow an object as much as a conventional parachute, but it can be deployed at speeds at which conventional parachutes would be torn apart.
The drogue parachute's simpler design allows for easier deployment. Where a conventional parachute could get caught in itself while unfolding or fail to inflate properly (thus not slowing the falling object as much as it should), the drogue parachute will inflate more easily and more reliably to generate the expected amount of drag.