It depends on the springs your running.Four lifts ago(add-a-leaf) I took off the clamps.It flexed like crazy but you had to realign the packs every few trips.Now I run the open style brackets and still look for better rear flex!
After my lift, I modified my spring clamps. It is loose enough top-to-bottom to allow some flex, but exerts enough pressure right-to-left (controlled by how tight you make the nut-and-bolt) to prevent/reduce fanning.