That developed not so much from common sense, but from centuries of fighting. That's really the only way one can find the most effective way to fight.
Anyway, I think Napoleonic soldiers were probably a lot more inclined to hold on to their equipment because, unlike Americans in the US Civil War, they often operated in foreign and hostile areas, where one wouldn't know the terrain and it'd be a lot harder to survive and get aid from the locals than it would be when fighting a war in one's own country. That makes everything you own a lot more precious.
I realise that southerners didn't exactly welcome Union soldiers (or northerners rebels), but I don't think their hostility was usually comparable to the kind you'd experience in a war between sovereign nations.