Accurate billing is extremely important when it comes to independent contractors and small business owners. You can't afford to lose a customer over something that should be done right the first time. Business owners who provide detailed, prompt invoices straight to the customer's inbox come out way ahead in the credibility stakes.
When you send an invoice with a file attached, your client will see a link to download the attachment in the invoice email message. If you send your client a link to view the Web Invoice in Harvest, they'll see the link there, too.