I was re-reading the rules of Call of Cthulhu (5th Edition) today whilst preparing an adventure and saw the knock out rules:
Use this rule to render a target unconscious rather than to do physical harm. The player or keeper should state the intention before making the attack. Perform Knock-out attacks only with Fist, Punch, Kick, Grapple, Head Butt, Clubs or other blunt instruments. Roll for damage as in an ordinary attack, but match the result against the target’s hit points on the Resistance Table. A success knocks the target unconscious for several minutes, and the target takes one third of the damage originally rolled (round down any fraction). If the attack succeeds but the Resistance Table roll does not, then there is no knock out, and the target takes full rolled damage.
As I understand the rule, there isn't any kind of trade off for using this kind of attack: Either you knock out an opponent for several minutes (big advantage because knocked out opponents can't do anything, and several minutes probably means the combat ends before the opponent awakes) or you cause normal damage. Provided the opponent is affected by the knock out (ie not a mythos creature) and you have a blunt weapon, why would you not always go for the knock out attack?