D7100 1.3x crop in sensor vs Crop in Software?

Mako2011 wrote:

But you frame different depending on the mode...so with the 600mm prime in normal mode you said you would frame the subject to use the whole frame ("...composing to fill the frame...") and you would do the same in crop mode to maintain say the 3rds rule. That would mean you need to back up when shooting that sparrow in crop mode with the prime or zoom out when using a zoom.

nfpotter wrote:
However, in the real world, most people (at least ones that think about composition) are going to frame based on things like the "rule of thirds", or "golden mean". SO, if I do that in full resolution, and I crop to a 15 MP image, I MAY be using pixels further away from center, than if I had used the same framing/composition already in crop mode. Both end up being a 15 MP image, but the latter used more pixels closer to the center of the lens, and thus a potentially sharper image, given the same composition.