I would like to see a history with the date, time, user, and a brief summary of the activity for each invoice. For example:
date time user invoice created
date time user invoice edited
date time user invoice emailed
date time user invoice paid
date time user reconciled
Our previous accounting program had this feature and it was very useful for knowing what the invoice status was and who made any changes. Because of this feature, I was able to determine the person at the accountant's office who had incorrectly reconciled several transactions of our income as household expenses (inexperienced receptionist).