Yeah, it's supposed to help immensely with axle-wrap, but like I said, traction bars will do as much or even more to combat that. The old 'slapper bars' (like my old school Lakewoods) will allow just a little bit of wrap, but once the bumpers engage the underside of the leaf springs, that's the end of that. The weld-in bars (like the Shelby Under-ride style, where the leading end of the bars actually weld to the torque boxes) act more like a two-link addition to the rear axle than anything, and wrap is pretty much non-existent.
I'm still not sure about staggered shocks, unless someone just doesn't want traction bars at all. And even then if it's for better performance, then why not toss on some traction bars. The aftermarket two/three/four link set-ups typically don't use a staggered shock set-up after all.
Having said all that, I'm no expert on this by any means. I just know a little bit about it and what makes sense to me. I'll be interested to hear what others have to say.