Any out?

I could probably make one at this point, I use them for tracked stats a lot.
EDIT: Nvm, I don't really know how to use them for normal skyrim purposes.

What did you need to know? They seem fairly self explanatory if you open them up and look at them. You can add remove using AddFaction and Removefaction functions.

just dunno what's the use , I see even bears do have a faction but I have no idea wha'ts the point ...

You can use them for all sorts of things - any time you want to separate groups of people. For example in my mod I want certain people, but not everyone, to start chanting when the player goes near them - but only at certain times of day. So I give the chanters a scheduled package which puts them in a Chanting faction for the duration, and my player has a cloak-type 'Start chanting' magic effect which only affects members of the Chanting faction.

Well you can use them to control who likes and hates who, use them for variables like getFactionRank to delegate various tiers in a faction, like baby vampire versus master vampire, and use conditions to apply this to your scripts. It is how you create a merchant, you add a faction that sells things to an NPC, etc. If you want the player to get in trouble, you add him to a faction that is the crime factions of the holds. All sorts of useful features with factions.