Used to be that inspectors here required only one cable per hole, but in the last few years they realized that this turned the framing into swiss cheese, and now allow two only. (Allowing two 12/2/2's) In the guiese of not exceeding 9 current carrying, as you would in conduit, same for stacker and other bundles. Taking a large bundle of cables, like some would above a panel into a single connector isnt allowed for these same reasons.
That said, if I go a few cities over, where bundling is ignored, you can tell the difference. You really can feel the difference in warmth in the bundles. And on occassion see a slight discoloration of romex sheathes in stuff installed around ten years ago.
