It affects your world view. Your religion, your station and even the basis for existing. The way your culture impacts your views is evident in your morality, your interpretation of events as superstitions and even, sadly, your view of other people. While it is not condoned, prejudice is a reality on some part to every culture. But by and large the purpose of the cultural origin is to determine similarities in the way a character might view something differently than another or the player themselves. It is a role-playing tool for both player and Arbitrator.
Many effects, such as shade realm magic, will be affected by the interpretation from your culture. From simple thoughts on the nature of the creature or the Shade to the existence of magic itself, this is determined by cultural mores. Portents and omens are likely to be viewed differently from one group to another.
The player should always relate to their cultural origin in some way when interpreting events. The arbitrator can even use this to help paint the picture in a way that two different cultural characters may interpret apart. This exploration of character and culture expands role playing potential and enriches the game as a whole.
Native born Praelians that survive are not rare, but uncommon. Their cultural origin is shaped by region they grew up in, but also by the parents of the Natural Born. (Even if unknown, the cultures should be generally known to the Arbitrator.
Native born Praelians are completely subject to the interpretation of the Arbitrator in these matters, and the source material for the regions.
In these cases, nature beats nurture every time.
