Read 110.14(b):
"Soldered splices shall first be spliced or joined so as to be mechanically and electrically secure without solder and then be soldered."
So if the solder can't really be used as a conductor, nor as a method to make the connection more secure, why even apply any solder? If the joint you make is mechanically (not going to come apart) and electrically (conducts current flow without excess resistance), the solder has no function.
I know of several ECs in my area that require their guys to S&T. In addition to testing the quality of S&T compared to wire nuts, I'd like to see speed trials as well. I used to work with a guy who S&T'd, and by the time he had a box made up and ready to solder, I had my wire nuts installed and was pushing everything into the box.
He, on the other hand, still had to come back with his torch and solder, heat the wires up, apply the solder, (being careful not to melt the insulation, burn a hole in the box, scorch the stud or catch his clothing on fire!).
Then, after that complete trip around the entire house, come back for
another trip around the house and wrap everything up with tape before he could put it all back into the boxes.
By the time he's got all this done, I'm down at O'Mallys' quaffin' beers, watchin' the game and sinkin' bank shots.