So, i always played with all doors unlocked in my households. Now after more than two years i decided to change that and now im locking all doors completely just out of curiosity and because some of m...
I've actually made 'rooms' to lock areas for sims either played or NPC to have access to or not. Other than the main entrance, I usually lock all other entrances/exits to all but household members.
Also, you may want to lock toddlers from going places you don;t want. For example you can keep them from wandering into the street by locking doors to just that toddler.