Per Paradox policy, each expansion of course must have a content pack - this one is pretty nifty tho and can be of good use!

The Conclave Content Pack for Crusader Kings 2 is an optional cosmetic-only DLC for the game, which confusingly isn't included in its parent expansion Conclave.

With this DLC you get extra 3D models for councillors (for example, a woman Spymaster would show up as a man on the map when placed on a province without this DLC), new portraits for characters of specific cultures (Finno-Ugric ones), and a few historical buildings have now unique 3D models (e.g. if you look at Gyza in Egypt, you'll see small 3D pyramids there).

From personal experience and general opinion I've observed, you usually want this DLC for the Finno-Ugric portraits. Not only they are well done, but they also replace the non-culture specific portraits that you get in the base game which are ugly to say the least. The remaining features are stuff you hardly notice.

The price of this DLC is on the steep side, particularly because it's 3 of them you have to buy to finish unlocking all unique portraits (the remaining ones are the Content Packs for Horse Lords and The Reaper's Due). However, WinGameStore consistently offers the best prices for Paradox DLCs, so here you can get them for what they're actually worth.