I have a champion juicer. I had it before I started making chocolate, and used it all the time. I think it cost me something like $350 CDN. When I first started "pre-grinding" my nibs, the burs were sharp. Within just a few uses, the burs were dull and more or less useless for anything.
I started heating the nibs, cocoa butter, and even the bowl and wheelsof my santha knock-off, and never looked back. Regardless of whether I preground stuff or not, it was still taking the same amount of time to drive off the volatiles. I wish I would have known sooner. It would have saved me yet one more damaged piece of kitchen equipment thanks to those rock hard cocoa nibs!
Most of the artisans I communicate regularly with on another forum have also stopped using the juicer (including the forum owner himself), as there is no real benefit found from it - just cost.
Now having said that, if you are simply looking at particle reduction, well.... I guess it could save time. However in my opinion that takes a backseat to flavour development, and to be candid, happens anyway when developing a good flavour.
Cheers.
Brad