I keep hearing that shackles and spacers affect the life span of coil springs and spring packs, but cannot for the life of me see why they would? As long as you have the range of travel, what difference does it make if a coil spring sits against a spacer, or the housing? Can any elaborate on this? Or is this whole thing just a myth.

Pretty much a myth.
A spring really has no idea how it's mounted to a vehicle.

That's what I figured. Thank you sir for your reply.