This is one of my favourite variations on the standard lateral raise.
When I've spoken previously about using mechanical tension to lift more weight or work muscles harder, this is my go to example.
By starting with the elbows bent at 90 degrees, this shortens the lever arm of the exercise aka It makes it easier to lift bigger weights (because physics, yo).
Once the arms are parallel to the floor, the elbows extend outwards as this extends the lever arm again.
Then coming down with control, not just dropping the weights down.
The shoulders are put through a lot more work on this exercise compared to a more straight arm lateral raise.
This is my, mostly, Personal Trainer musings and information which I hope you'll find helpful!