When you work your back your working all those muscles at the same time ...Now form has alot to do with this As well .For example if I want to go for width on my lats I want may outer lats to get the pump not my arms ..So I will use straps for all my back work .This will help you focus on your lats and your back thickness without worring about your arms or grip failing before your back does ...Now as far as deadlifts go straps wont help to much with your arms getting worked or your neck or your shoulders ...Deadlifts are just a huge mass builder working everything at once ..CDOG