I think every adventurer expects looting. Looting is how adventurers make their money. And yet in modern times, looting is considered dishonorable. So I’m always torn. Is looting moral or immoral?
First, I will insist that it depends on the culture. So everything said here is perception - there is no reality! Having given my disclaimer, I know several men, each of whom I respect wholeheartedly, who happened to come home from WWII with things that he didn’t exactly have issued to him. There may be a katana (modern infantry officer’s weapon, not some ancient work of art) I know of, and a gorgeous SS Officer’s luger. (Of course these were from different men.) So were these guys in the wrong? Definitely if you read the modern codes of conduct. It may be decades of playing FRPGs, but I think there is a line of morality. Taking something off a dead foe is one thing; taking something from a scared civilian family is another. Further - trading with a conquered foe is really OK, even if he’s selling his equipment in order to buy food.
Was it always morally questionable? Absolutely not! Caesar intentionally hit targets rich in loot in order to keep his troops happy (and prosperous). Not only did they loot the valuables that they came upon, they tied up the people and sold them to the slavers. The taking of slaves is one of the biggest forms of loot, and yet something I haven’t seen anyone do in any style of modern game. I guess it’s just too politically incorrect to even think of enslaving someone for profit - but again, I think you need to consider the culture.
One of the biggest questions I have, and I don’t really know the answer, is what you do to make sure the officers or nobles get their cut. I think they just get to wander the camp and anything big enough to catch their attention becomes theirs. There are probably noble houses or palaces that are off limits to the rank and file and only get to be looted by the bosses, who then give the things they don’t want to the soldiers who helped them loot the really good stuff. After all, if the noble officer takes a marble statue and a golden statuette, he would probably be willing to give his brute squad the solid silverware, which is probably much better than the rank and file got.
Does it matter? I think as a world builder, you need to establish what is considered acceptable behavior. Is it OK to loot civilians? Is it OK to capture and sell slaves? Is it OK to loot temples? That one got a lot of folks in trouble in the ancient world. Once you determine what is allowed, you have to establish the buyers for this stuff. If looting is not allowed, then there would still be a black market. This won’t get the looters anywhere near as much as they have gotten, but it’s still probably worthwhile. You also have to think it through. If looting of enemies is not allowed - what happens to all their stuff? Are they buried in it? Does the “army” take it? and if so, what do they do with it? Leave it in the field, and there will be looters, maybe the dregs of society, but someone is going to be willing to try and make a buck off of it. Ah, the unintended consequences of laws trying to mandate morality!