Hi and welcome to the website :)

For the Osprey, the main purpose of pro-rigging the bait is to make it last longer. The action if you fish the stock harness vs. the pro-rig should be exactly the same. When you pro-rig, the lure will typically slide up the line during the fight, and that way you can get 2 or 3 times more fish per bait.

The Osprey harness has changed a little over the years (the newer ones have a metal disc welded on to the wire harness) and they certainly appear like they will last longer than the old style but regardless, if you want more fish per bait, pro-rig it.