Invoice No.(Invoice Number): To stay organized and make the tracking easier for your tax season, we strongly suggest providing unique and sequential invoice number for every invoice you send.
The best thing about using an invoice system is that you can track your time against the amount you're getting paid for each task. In order to run a successful business, you want your hourly rate to be profitable so you're not losing time and money. Another benefit of using an invoicing system is that you'll never save over an invoice and lose the work you've calculated for another client.