The first, the supreme, the most far reaching act of judgment that the statesman and commander have to make is to establish … the kind of war on which they are embarking; neither mistaking it for, nor turning it into something that is alien to its nature.[2]

[2] Quoted in John T. Fishel & Max G. Manwaring, Uncomfortable Wars Revisited, Norman: (2006) Univerity of Oklahoma Press, p. 9 from Carl von Clausewitz, On War, translated by Michael Howard and Peter Paret, Princeton: (1976) Princeton University Press, pp. 88-89.
From brother Fishel's book review, Thinking and Writing About COIN.

In any given instance, the materiality (weight to be given) re: the enemy's policy and strategy has to be determined. IMO: e.g., we blew it in Vietnam by not recognizing the kind of war Ho-Giap et al were fighting, compounding by supporting a series of failed SVGs - all determined by trying to force the war into the mold desired by the USG.

In a much simpler (and non-lethal) context, your last section's questions apply to any lawsuit - decide what is material and what is not. IMO: that's largely a matter of experience and intuition.

Regards

Mike