NPC's are the lifeblood of many adventures. Be they the shopkeepers, the townfolk with a problem, or the lonely ogre in the dungeon. An NPC that comes alive can be a joy for the players to interact with. A fun time that they will remember and talk about for years to come. Alas, most adventures don't contain THOSE NPC's. Instead they contain boring NPC's with too much backstory and irrelevent physical detail.
The typical shopkeeper perfectly represents several of the principals of good adventure design. A typical one might be something like:
"Mary & her husband Jorg came to town eight years ago. After working for the saddler they saved their money and opened The Rough Saddle. Mary is 32, blond with a stout figure and a kind face. Jorge is seldom seen, working in the kitchen cleaning dishes and making stew. He is 33, black hair, and has a fair complexion."
Note here the backstory that (presumably) doesn't contribute actively to anything in the adventure. And the physical features that are, essentially, common. This adds nothing to adventure and just takes up space. It's just the normal sort of filler stuff that can be inserted on the fly. If Jorge was NEVER seen, or had leprosy, or Mary was bald and didn't know it, then we've added something for the DM to hang their hat on.
This feels a little like I'm putting several principals together to show how they operate to a cohesive whole.
