Players should take the opportunity to occasionally befriend monsters instead of trying to kill them while playing Dungeons & Dragons.
Last night, I ran a Holiday one-shot for my Dungeons & Dragons group, in which adventurers attempted to find a group of missing children who disappeared during a Yuletime celebration in a remote village. The villagers immediately blamed a nearby coven of hags who lived out in the woods, as hags are evil, are known for kidnapping and eating children, and are....well, they're hags.
The clues certainly pointed to the hags as the culprit, but at least one of the players realized that something was amiss. And so, when the adventurers gathered outside the hags' cave, the party's bard convinced over half of the party to carol for the hags instead of charging in with weapons drawn and spells singing.
That decision turned what could have been a standard D&D encounter into an extraordinary one. After a pair of fantastic Performance skill checks, the hags (a bickering duo named Brunhilde and Nestar) invited the party inside for some hot cocoa and conversation. While the hags did indeed have a single child from the village, they had "rescued" her from an even greater threat - an ice lich who planned to sacrifice the children in order to break an ancient curse keeping it in the valley.
Brunhilde and Nestar were delightful to roleplay - a pair of catty hags who loved gossip about the nearby village and bragged about the weight loss they had achieved since they stopped eating children over 500 years ago. The players had a blast hearing my terrible "Craig Ferguson as Angela Lansbury" accents, and I had fun spontaneously transforming a combat encounter into a social opportunity.
In the end, one of the players traded their future child (his character in our ongoing "main" campaign) to the hags in exchange for the child they had rescued, and the hags gave the player a valuable pendant that proved useful for their encounter against the adventure's true threat - the ice lich known as Frosty the Snowman. Not only did a throwaway encounter provide sudden character development for our true campaign, the players also avoided wasting spell slots and potions on monsters that didn't need to be killed.
Encounters like this reminded me of the importance of giving players opportunities to befriend and interact with monsters. While a monster's alignment might be evil, their motivations or goals might not in total opposition to those of the players. A solid Persuasion check or some clutch roleplay might turn that young chromatic dragon or that hag into an ally...or at least push out a combat encounter for another day.
Not only do friendly monsters provide unique roleplay opportunities, they can also be utilized as a fantastic resource. Maybe they can be a source of useful information for the party, or maybe they can act as a spy against the "big bad." Plus, if you do decide to have the monster eventually return to their base instincts, it will make their sudden but inevitable betrayal that much more tragic and heartbreaking.
So - the next time you see a troll not actively terrorizing humans in the woods, try talking to it instead of putting an arrow through their eye. Maybe, just maybe, that troll will turn into your best friend or save your life later in your campaign!