I suppose what I mean to say is that some hints might help with the creation of a character. Without really knowing the state of the world we're to be playing in, it can be a bit difficult to give a race, class, or individual any real meaningful context.
Then there are the little mechanical things, such as whether certain enemy types will ever make an appearance. There are a few classes in the Book of Vile Darkness, for example, that deal with slaying and combating Aberrations, which becomes rather useless if the campaign never encounters any. Of course, that could simply raise some interesting moments of its own--how will a warrior dedicated to hunting a single type of foe adapt to being faced with ones he has no experience with?
A bit of perspective might make things easier, is all.