Just to spell out the obvious, I think the two biggest things to consider for norms-shaping include
a. the costs of this norm. In this case, lack of military necessity means the direct costs of the norm can’t be very high, at least if we think of states as rational-ish actors. There are also coordination costs to consider, as you say.
b. the benefits of this norm. Where abstract notions of just war is one answer, what the Gods want is another similar answer, to curb the worst excesses of war is a third answer, and the answer I favor in terms of both explanatory power and normative force is to allow wars to end earlier, which the literature calls the “duration-multiplier argument”. I believe my answer might actually be the oldest.
Just to spell out the obvious, I think the two biggest things to consider for norms-shaping include
a. the costs of this norm. In this case, lack of military necessity means the direct costs of the norm can’t be very high, at least if we think of states as rational-ish actors. There are also coordination costs to consider, as you say.
b. the benefits of this norm. Where abstract notions of just war is one answer, what the Gods want is another similar answer, to curb the worst excesses of war is a third answer, and the answer I favor in terms of both explanatory power and normative force is to allow wars to end earlier, which the literature calls the “duration-multiplier argument”. I believe my answer might actually be the oldest.