As far as I recall, they were explicitly created as a fun idea and a semi-challenge to at least somewhat give an out-of-context threat to the west.
Also, I would also add that Conclave beats my other suggestions in "really recommended", but it's apparently been somewhat divisive.
It's divisive in the sense that people really did not like defensive pacts, which was a free feature unrelated to Conclave itself.
It carried over into the DLC itself, and these days if you find someone bashing Conclave they're oftentimes players who don't know how to play the game.
Conclave when fully utilized makes 1. realm management easier, 2. law changes easier, 3. intereligious interactions possible, and 4. Vassal interactions more in depth.
1. War Council is very powerful in that it (oftentimes) locks you 7 most powerful vassals from factioning, resulting in an exceedingly stable realm. That's not even including the non aggression pacts you can form with the other vassals to easily lock over 60% of the realm from factioning. You can do the same without Conclave, but will require a lot of children.
If you choose to forego War Council, Absolute authority gives you +2 desmense over normal gameplay, which can be huge.
2. Regarding law changes, in the base game this is determined by a vote from every lord in your realm. If you are particularly large and the law is particularly unpopular, this can take an entire generation to get that last level of Crown Authority.
Contrast this with Conclave where you can either instantly pass a law via absolute authority, or instantly (at most a year of deliberation) pass a law with a vote between 8-10 people. 8-10 is a lot easier to bribe than 100.
3. Religious interactions. Want a claim on the Byzantine Empire as some Emir in Baghdad? Buy a favor off the emperor, force a marriage with his daughter, and wait a generation. Your kids will all have a claim on that title, and that entire realm when the princess dies. In the meantime you have the Emperor as a possible ally to assist you in your other wars.
Invite the last Merovingian to your court, extending the bloodline or pressing his claim. Or as a Christian for whatever reason invite a Muslim Sayyid and breed that trait into your line.
Fear for your life from close proximity to Seljuk or the Mongols? Again force a political marriage!
4. Favors also help in other less important matters like getting your liege to press your claim for you, asking for a pardon, getting him to start a vote, getting other vassals to join your factions or vote your way, etc. A
lot of interactions.
And yet people who generally complain of Conclave generally don't appear aware of these perks.
