Fighter: "Remember, we don't want to kill them, we should do non-lethal damage to them, we want to question them afterwords!"
Ranger: "Agreed. Wait. They have an AC of 30, I need 14s to hit them with my bow and I have weapon focus, and a dex of 20. I have a strength of 10 and no magic melee weapons. I'll need 20s to hit them, even if I don't take the -4 for doing non-lethal. Guess I'll roll a dice each round in the hopes I roll a 20. If I DO hit, I'll do 1d8 non-lethal against a creature with 81 hitpoints."
Fighter: "Well, you could always just keep shooting with your bow, and I'll be doing non-lethal. Then, hopefully he won't die."
Wizard: "What do I do? I can't do non-lethal and none of my spells are non-lethal."
Fighter: "Do the same thing as the Ranger."
(2 rounds of combat later)
Ranger: "Woo hoo...I crit, I do THREE times my normal damage. That's...58."
DM: "Alright, that puts him down. Unfortunately, he had 1 hitpoint left. He's taken 40 points of non-lethal, 40 points of lethal and he had 81 hitpoints total. The 58 takes him to -17 with real damage killing him."
Fighter: "What did you DO? Remember, we wanted him ALIVE. How are we going to figure out who killed the King now? He was our ONLY lead! How could you be so stupid?"
Ranger: "I'm sorry, I didn't mean to roll a crit! I just got lucky!"
Fighter: "There's nothing lucky about that crit!"
VS
Ranger: "I hit, I do 27 damage with my attack."
DM: "That drops him, would you like him dead or unconscious?"
Fighter: "Remember, he might be the only one to know who killed the King, keep him alive."
Ranger: "Alright, unconscious then."