This is a relatively advanced position of rotator cuff strengthening. The supported nature of the exercise allows larger prime movers of the shoulder to reduce their input, which leaves smaller more stability based muscles to have a larger influence on the performance of the exercise. Being in abduction and rotating from this position is an unstable position of the shoulder and therefore this position needs building in to, a good starting point can be the Sidelining Shoulder Lateral Rotation.
Tightly grip the weight
Keep the shoulder blade slightly pulled back & up
Rest the elbow at around shoulder height
Targeted muscles trained
Key movements trained
Shoulder lateral rotation
Rotator cuff capacity
To increase the stability challenge and expose your shoulder to a little more compression you can rest your elbow on something like a bar, at shoulder height. This can be considered a progression compared to the position in the video which is accessible but slightly lower than the shoulder.
Having your elbow in line with your chest will also increase compression in the joint, which is ok if you are wanting to subject a progression in this way. It also increases the work of infraspinatus. Whereas having the elbow in a forwards position compared to the shoulder will increase supraspinatus work and reduce compression in the joint. Which you choose will depend on your goal.