The cable cross-over is an isolation movement that uses a cable stack to build bigger and stronger pectoral muscles. Since it's done using adjustable pulleys, you can target different parts of your chest by setting the pulleys at different levels. It is common in upper-body and chest-focused muscle-building workouts, often as a pre-exhaust at the beginning of a workout or a finishing movement at the end. It is often used in combination with other presses or flyes to target the chest from different angles.