How to Use the Outfit Management system.
Original post on Shrike's Blog

If you are using SKSE and SkyUI then you are in luck!
Anna NPC’s now has a Outfit management system that can be enabled through the SkyUI Mod Configuration Menu.

Once the Outfit Management is enabled for a specific follower the options become available in the dialogue tree.

First!!  It is important to know not to use the outfit inventories as storage.
Only put items in there you want them to wear.
If you want the follower to carry loot and items for you then use the Carry Bag option:
“Would you carry this in your bag?”

The Outfit Management options are available under the topic:
“Let’s talk about your clothes.”

Available options are:
“About your weapons and armor.” (All)
“About your casual clothes.” (All)
“About your fancy clothes.” (All)
“About your sleep wear.” (All)
“About your underwear.” (All)

“About your mage clothes.” (Anduniel, Valyen)
“About your thieves armor.” (Anduniel, Darion, Mareen)
“About your imperial armor.” (Elyndra)
“About your companions armor.” (Nadina)
“About your daedric armor.” (Teryn)
“About your Dibella robes.” (Zorya)

Now what do these inventories do?
Well there are a few options.
If you keep the default option (recommended) “You can wear what you like.” they will then automatically change outfits depending on where they are and if they are in combat or not. Below is a list what they will wear and where.

Option “You can wear what you like.”
Casual clothes will be equipped in following locations:
♦ Inns.
♦ Player Home.
♦ Walled Cities. (Markarth, Riften, Solitude, Whiterun, Windhelm)
♦ Most interiors in walled cities.

Fancy clothes will be equipped in:
♦ Jarls castles/homes.
♦ Custom locations with keyword LocTypeCastle.

Sleep wear will be equipped when:
♦ Sleeping.

Underwear will be equipped when:
♦ Swimming.

Mage Clothes will be equipped in:
♦ College of Winterhold.

Thieves outfit will be equipped in:
♦ Ragged Flagon.
♦ Thieves guild head quarters. (Cistern)

Imperial Armor will be equipped in:
♦ Castle Dour. (Solitude)

Companions armor will be equipped in:
♦ Jorvaskr.

Daedric armor will be equipped in:
♦ Jorvaskr.

Dibella Robe will be equipped in:
♦ Markarth.
♦ Most Markarth Interiors.

♦ If they are in one of the above locations and combat starts they will change to their armor.

♦ If they are not in one of the above locations they will wear their armor.

Option “Wear your xxxxx outfit/armor please”
♦ They will then equip that outfit and only change to their armor when combat is beginning and change back when combat has ended.
♦ Except for the Imperial, Thieves, Companions and Deadric options. (Because those are armor)
♦ They will not automatically change to casual, fancy, sleep or swim outfits.