It doesn't have to be mechanical, but it can be. And in some cases mechanical options can help drive home the point of that culture/nation/faction, and help a character from that faction stand out.Edit to add: 3) Why there has to be anything mechanical connected to it (aside from some recommended backgrounds that might come along with each)
Do they have a goatee?I am puzzled by this fancy debate over culture and background. Are you evil and can I kill you and take your stuff?
Agreed, it's as easy as that.All I care about it that in Menzoberanzan, evil drows are in charge, and everyone (who want to live) play by their rule. In this setting, Menzoberanzan is the enemy, with all the yuk and moral crap that goes with it. And I hope that my PCs will rise above that
The problem with factions is that they are setting specific. I have factions in my campaign world that follow Fenris (aka Fenrir depending on how you Anglicize it) the wolf. The highest honor is to become werewolves, and the truly powerful ones become far deadlier than your typical lycanthrope.
Which works great for me, makes no sense in FR. As far as monsters, I think we should go back to "often", "frequently" and so on for alignments. But that's been hashed to death.
Race, subrace.
Background, culture?
Class, subclass.

(Dungeons & Dragons)
Rulebook featuring "high magic" options, including a host of new spells.