In this case, the enemy was a hobgoblin. An evil creature intelligent enough to be dangerous, strong, brutal, cruel, and a hated enemy. It can see in the dark, so if it was captured, the group would have to constantly watch it. It is likely as strong as any warrior in the group, so even unarmed, it would be a threat to say, the mage or possibly the rogue (ie, the weaker group members). It could signal to nearby allies watching them, or escpe and inform others about the group, providing exact numbers, strengths, weaknesses, and all sorts of other information it could gather. And at night, it could help any nearby allies ambush the group or sneak in by signals, expressions, etc, that the group would be none the wiser about, disable the watch and kill the rest of the PCs in their sleep. Not to mention, it could resist them, slowing them down by forcing the PCs to drag it along as dead weight. It could argue, bark, yell and otherwise distract, or shout for reinforcements, help, etc.