What does the PVA Nugget do, prevent tangles ?
The main reason is so that if the bottom bead moves, or if you are only fishing a couple of inches above the lead, the hook won't get blunted if it knocks against the lead.
But it also gives me peace of mind that there will be no tangles (I know that Newmarket says helicopter rigs don't tangle, and in the main this is true, but there is always a chance that it hits the water at a weird angle and gets wrapped up) and the rig will present itself nicely.
And the final reason is that when the nugget hits the surface you have something to aim for if you are putting in some freebies around your hook bait.