The Automatic Choice Selection permission changes the way that partners view effort stats, so that they are no longer limited to seeing orders and revenue for choices they have specifically been given access to. Instead, they will automatically have access to all choices on the effort's offer as soon as they are assigned to it.
Even if something were to change the choices available to the effort, such as if a new offer is assigned or if the choices on the offer are changed, a partner with Automatic Choice Selection will automatically update have the new choices selected.