I begin to understand the difference between “Independent association” and “Foreign key association” in Entity Framework Code First thanks to this article : http://www.ladislavmrnka.com/2011/05/foreign-key-vs-independent-associations-in-ef-4/
Advice: use both (Independent associations and Foreign key associations):
“This saves on unnecessary DB lookups, allows lazy loaking, and allows you to easily see/set the ID if you know what you want it to be. Note that having both does not change your table structure in any way.”