Back in the days before e-commerce, every job was billed using paper invoices, everyone was paid with paper checks, and all those paper records were delivered in person or sent in the mail. Back then it was easy to put together the information needed for an invoice. For the self-employed freelancer in the 21st century, things are no longer that simple and it affects what you put on your personalized invoices.
Most businesses use the same sorts of information on invoices: contact information, sequential invoice numbers, etc. Because of the unique nature of freelance work compared to other businesses, especially for freelance invoices, it should be adapted to reflect these differences.