According to my little book of exercise anatomy, which includes nifty pencil sketches with targeted muscles colored red, says…
“This exercise works the upper trapezius and medial-posterior deltoid groups most intensely… The wider your grip, the more the movement works the deltoids and the less it works the trapezius muscles.”
I find it a great way to balance the ease with which I can develop the anterior deltoid compared to the other shoulder muscles.
I’ve also read somewhere that your delts are recruited until your arms are raised laterally, then, as you continue to lift for that final few inches, your traps are used to continue the movement. It’s not in my book though.
Anyway, consider getting yourself a book like this. It really helps when considering how to balance your development and it really highlights the grip or foot placement variations that you can use to shift what an exercise targets.
Finally, it issues cautions for various exercises, based on common injuries, and how to avoid them. Be smart, lift for life.