When an Invoice is voided it often times is un-known who voided that or why it was voided. This is the case in a business that has 5+ employees.

Example: A field tech creates 2 invoices and voids 1 of them. The office staff does not know why 1 was voided.

Thus a "Notes" field when editing or voiding the invoice would help with this. Many other billing systems have a "Notes" field that can be edited and seen after the invoice is closed out.