The Reasoning

Nonlethal damage is a clunky mechanic from the old editions. It's exactly the same as normal damage unless your combined lethal+nonlethal exceeds your HP, at which point you simply fall unconscious rather than dying. In other words, for the most part dealing nonlethal damage is completely indistinguishable from dealing lethal damage. The major difference is merely that it is easier to heal, healing 4 points of nonlethal damage for every Reserve Point spent. This is almost entirely an out-of-battle difference, however.

Saga rules make the difference between lethal and nonlethal damage important and recognizable in battle. Stun weapons deal less damage than their lethal counterparts, but they are much more effective at moving an opponent down the Condition Track.

The Rules

Nonlethal damage no longer exists as a separate damage type. However, weapons can still be nonlethal in nature. Weapons wielded to subdue do only half their normal damage to the opponent's HP. However, the full damage rolled is used to calculate whether or not the attack exceeds the target's damage threshold. If it does, the target drops -2 levels on the Condition Track, rather than -1.

Creatures which are immune to nonlethal damage still take half damage from a weapon when it is wielded to subdue. However, it otherwise works like a normal weapon, rather than a subdual weapon - the actual damage dealt is used to check if the attack exceeds the target's damage threshold, and it only moves the target -1 levels down the Condition Track rather than -2.