Everyone has a camera on a device that can send emails. Unless the internet went down and for some reason the phone system still worked, I can't think of any scenario where fax is better than emailing photos.
Legally, this is interesting because it doesn't exist in email. You had the machines agree that the complete document was sent and was received. You will certainly find that it other transfer protocols, but not email, where the machines don't talk to each other directly.
Also, even when you have both an internet connection and a camera, there remain numerous possible reasons why you may not want to use the internet to send certain things.
I'm certainly not saying that everyone should start faxing, but I totally understand why there may be a substantial minority for whom it makes sense at least from time to time.