In 2005 we had around 14,000 worth of rock damage on a new Lexion.    In Navy beans ya open everything up and slow everything way down in the combine = worthless rock trap.  We pick rocks, but not anything smaller than my fist......usually.  We dont row crop cultivate anymore either.

In 2006 we bought a 23,000 dollar 50 foot roller.    Can do 500 acres a day easily.     Now pick less rock, combine a tad faster due to less pushing, and haven't had any rock problems.

I would never claim a yeild increase, but I do think its a cheap way to insure combine capacity during harvest.   Were very happy with ours, but wish it was 10 feet wider to follow the planter tracks.

Good luck