What is the difference in having this enabled for the device?

I thought that is how it was communicating in the first place, by sending
sms messages to the phone each time there is an email and then deleting
them. Yet there is the option to enable it for the client after you "sign

I have tested it with it not enable (default) and then enabling it (giving
it my phone number - it sends a message and gives me a code, I plug the code
back in). And don't notice any difference.

Please enlighten me !