Are concubines worth it in CK3?

[Bison]

Unlike CK2 where they could give you decent amount of prestige up front that you could then use to build tribal holdings, it seems in CK3 they only give claims for you children which frankly i would say arent that usefull when you play as tribal (unless you reform pagan faith of course) as when you have enough prestige and fame you can pretty much conquer dutchies and kingdoms.

[Duilf]

The short answer is no.

One common thing people forget about when it comes to culture/faith is that it applies to everyone with those qualities. Concubine kind of like Warmonger is great for the player who has the mindset to control it properly, and terrible for their realm who will not. The player can use concubinage to breed in traits, and more safely breed into their own line as many of their kids are already only half siblings. The AI pays no attention to this so any good traits your vassals acquire will likely be breed out not in. Then there is the kids issue concubines mean extra kids which is bad under a partition succession law.

If there is any confusion about Warmonger let me clarify. Again the whole religion gets an at peace penalty instead of at war penalty. This means vassals with territory, or their own vassals of the religion have to constantly war, raid, or be subjugated to rebellions. Bare minimum this will negatively effect tax income.

[Duilf]

By breeding into their own family I am referring to https://ck3.paradoxwikis.com/Family_(relation)#Inbreeding
Basically breeding half siblings, or the children of half siblings is massively less risky then full meaning people can breed traits in their own line with their own family a generation earlier.

[Apoloyn]

Look.

If your trying to have kids with your wife and are unsuccessful, just try a different position. It worked for me

[Razorblade]

Generally speaking, more children is always better. More extra lives and more potential alliances to keep your vassals in-check.

[VoiD]

It's OP.

Concubinage > Polygamy > Monogamy

With concubinage you can endlessly expand your close family, and get concubines for your dynastic vassals so they can expand their own, so you can use even more family members to hold extra lands you conquer, you can also raid/siege kingdom capitals to get valuable hostages, like their daughters, to get access to powerful claims capable of taking over entire kingdoms or empires, even from different religions, with ease, plus, if you're trying to create powerful heirs you can have 3 extra partners having children trying to get the best heir.

Polygamy can't easily steal wives but it's still useful for everything else, and better at creating a TON of alliances within your kingdom and/or with external targets.

Meanwhile Monogamy feels like nothing but a handicap, you get one bonus for your first marriage, hardly relevant, and then that's it.