I alway's run them when doing a shackle and hanger drop.
When I did the 4/6 drop on my '98, I found that I didn't need them. So when I did the 2/4 drop on the '97, I didn't bother to check. I do have a bit of vibration, & I do have to do the universals. They are the originals, with 135,000 miles on 'em. I don't think that the drop had anything to do with their demise.
But you say that you always use them in a shackle/hanger drop. It seems to me that the 4/6 drop would have more effect on the pinion angle than the 2/4. I'm learning as I go. Maybe it's the way I picture it in my head.
The 2/4 drop causes the pinion to rotate which way? Up would mean the wedges go in from the back to cure, down would be from the front.
Do you use longer spring center bolts due to the thickness that the wedges add? Or are the stock length useable?