Originally Posted by ImportConvert

...and what do you base that on?

Please explain why you think this makes any sense.

When you get dozens (hundreds?) of moving parts that mesh together (modern car's drive-line), they have high and low spots on them. When you gently polish those parts down, the contact area increases greatly. They can then withstand greater shock, etc. because the contact patches are larger and the forces are transmitted more proportionately across the entire contact patch.

"Breaking it in rough" only means that you beat the **** out of it and those high/low spots may impact/mesh harder causing more deformity and material loss than is necessary, leading to a louder driveline, and other things that one doesn't necessarily find optimal.

Blogs written by some idiot a few years back have led to people doing this, but I owned a car that had a crate motor broken in by some old-school mechanic that thought like that. It used 1 quart of oil every 1200 miles (15-40, at that!).

Instead of this, why not look at how high-end cars are broken in at the factory, and how expensive engines for large machines are broken in. There is a definite "method" used, and it's not "be rough with it". Nissan included this break-in proceedure for a reason, and it's not to gain 1200 miles of "easy" driving so as to cut down on part replacement costs. It's so that they get less complaints about NVH, oil consumption, etc. during the next 2.9/34.8.