In UGG, one of the most appealing aspects of the game was playing though a battle and the computer remembering each phase, or to be able to roughly remember where your units were for the next phase.
This works for Shiloh as CSA, but is horrible for Union. CSA can push push push and every phase will remember just fine, but I hate playing as union and not only holding the ground but repelling and countering the csa, and suddenly be jerked back to the next position - not holding my formation etc. I had great positions in both areas, and then suddenly my units all teleported to the landing in a royal mess.
If we are being allowed to change history, we need to have some flexibility in the phases during the major battles.