That, and you could also lay more weight on the cohesion related advantage of columns. To add to what Didz so nicely summed up: We could ask people on the street with no military training at all to form a three men wide column and march them through the city in good order. A column seems like the "natural" form of a group of people who desire to move jointly. All you have to do is follow your man in front. That helped especially people's armies of the latter half of the ETW era, like the armies of the American colonies or the French revolutionary armies. Without warrants and scholarly quotes, I'd say, columns became so fashionable in the Napoleonic era because of their simple aptitude for "natural" cohesion, even with recruits or armed citizens who are shot at for the first time in their lifes.