I can see this being useful for anyone who pays for a second phone line for a fax machine. HelloFax invites you to throw away your fax machine and use their service instead.
Upload files from your computer to send.
Received faxes are sent to you via email.
I threw away my fax machine a long time ago, and replaced it with a printer/scanner/copier. Whenever I’m asked to sign something and send it back, email works fine — I just print the document, sign it, scan it, then send back by email.