Performing any sort of strength exercise with one limb at a time has several advantages over the usual bi-lateral work with a barbell or machine. Primarily it activates core stabilization. It comes much closer to “functional” work, as most of sports action occurs using one limb. You also can focus more effort in the lift, identify imbalances and use the other limb to help “spot” yourself. Dumbbells (or kettlebells) are the only equipment you need beyond your bodyweight, making these movements more “portable” and accessible.