Is there a story behind this?
I can't count the number of times the party has defeated the enemy, leaving one alive for questioning. Whether tortured or not for information doesn't matter, but it always comes down to what are you going to do with him when you're done? You can't let him go, even the LG party members are against that, but you can't really slit his throat either (as logical as it might be). It's likely he's evil, more so if you captured a monstrous humanoid (goblin, orc, gnome, etc.), so why not leave him tied up and walk him down to the slave auction, get a few gold for him. Orcs make good gladiators, and goblins make good fodder.
Most recently my barbarian challenged an orc warlord to leadership of the small goblin tribe, and won. I was left with the challenge of trying to figure out what to do with 40ish goblin followers who are lazy, disloyal, thieves, and murderers. I can't just leave them, they'll start attacking towns and such. And if I take me with them, the party is likely to wake with Colombian neck ties. I used about ten to disarm traps the fast way, but still had 30 left. Would have been great to march them all down to the market and sell them off to shepheards looking for variety (or whatever). They ended up being great fodder, and I'm down to 11.
Edit: Oh, and wouldn't be more interesting if the PCs were interested in more than just slaughtering their enemies. Using their resources to neutralize and capture their enemies, and then being rewarded for their careful planning, and cunning tactics... in the form of extra gold from the sale of monsters, beasts, and humanoid prisoners. And think of the potential of escaped slaves seeking revenge!