How much should we know ahead of time?

[BigDuke66]

Personally I usually read the "prelude" to the battle, that means reading on what led to the campaign, the campaign itself and the battles that were already conducted up to the current engagement.
That is simply to get the feeling of what my and the enemies forces went through, that may even improve gameplay because usually our experience has impact on future decisions and if that was so with the real life commander it may also be so with the "virtual" commander and he may even do the same things out of the same reasons that the real life commander did.
Of course the battle itself isn't in any way touched by me until it is finished.