Off-set Spring question

Does anyone know if you use the off-set shackles on the ends of the springs, do you have to use the spring relocation kit for the fronts of them? In my opinion if you use just the shackles wouldn't it put the springs in a skew on the spring perches?? Or is just a way to gain a few fractions of an inch for tire clearance?
I have a set of springs that came with a rearend I bought and they came with off-sets on them. I have a local place that can rebuild the springs for less than buying them on the net but before I have them rebuilt I want to make sure I either stay with the original shackles and keep them straight or maybe the off-sets give me another option? Feed back definitely needed..
Thanks!