I've looked around for info on the use of keys, but can't really find anything that details why they are needed. I'm thinking only to keep thieves out, but do thieves really enter houses? Maybe if your house is in a town, it would prevent npcs from wondering in....but my mod is in the wilderness.

Is their a reason to set this feature up?

To require the player to complete some sort of quest and/or to pay for the house.

Yep, I knew that one for sure. But why do NPCs living in the house need keys? It seems like once the player goes through the acquiring house stage, it doesn't serve much purpose, or does it?

I cannot answer that one as I haven't observed it. As far as I can recall, none of my followers have keys to player home(s). It may be that:

1. Because they are followers, they get ported to your interior location without ever having to pass through actual doors, or

2. Once the door is opened, any NPC who can open a door can open the player home door.

To test this, you could try a couple things in game:

A. Make sure a follower does not have a key in their inventory to your home

B. From outside, tell them to "use" the door to your home and see what happens.

I've noticed that some NPCs who have scripted interactions with the player can result in them "following" the player out of an interior cell in order to finish giving you their lines. It may also work going IN to interior cells, but I don't have a clear recollection of that.

You could use the console to create a need for a courier, then spawn the courier right next to you, and when he starts yacking at you, tab out and go into yours house . . . actually courier might not work, it might need to be some other NPC, but you get the picture.

There are probably a few experts on how all of this is programmed who will post in a bit and clarify all of this and save you the guess work.

Yeah, still need the what is the purpose of this answered if anyone knows. I want to assess if this is really important to implement for my own player home. I know it's used mostly to give the player access initially usually because they bought the home.

But I think you are right that followers can enter freely, I'm assuming because they have become a part of the Player Faction. Followers in game are not going to have keys. The only way to get keys to actors is if they are placed in inventory via CK, or there is an interaction in game that gives an npc a key, similar to giving a key to player.

As far as I know, thieves only steal anything if they're the player. I have a vague recollection that was done to prevent guards killing quest-givers with criminal bias. In Oblivion, City-Swimmer was often killed for stealing food.

Most of the use of keys in game mechanics is to allow NPC's to lock out the player at certain times of day. The CK wiki explains it http://www.creationkit.com/Locking_and_Unlocking_Doors

I had read that. I just see a lot of house mods using this, and giving npcs living there a key, so I wondered about the pupose.

I do see thieves commonly entering the trade goods market in Riverwood causing a ruckus and guards chasing after him. But that was during store operating time so they basically just walked in.

without the key, they can't pass through a locked door. it's as simple as that.

Right, s70, but why lock the door? I'm trying to get to the reasoning behind locking doors to begin with, aside from an initial quest to give the player access to the house.

mate it's KEYS for DOORS, seriously now

you lock the door so the player (or anybody else) can't go in.

you give the owner a key so he can.

that's it.

to that, with no locked doors, pathing would consider whatever is between the (now non-)locked doors as a viable route and you'd have khajit caravans, goat chasing bears and thalmor patrols wandering in and out your living room (and quest markers pointing through it) all day long.

so...? - dunno, but i really fail to see the oddity factor about keys that has you going about it?

edit: ok maybe no goat chasing bears, they both can't open doors by default. but how about bandit chasing necromancers?