What's the point of 2-factor authentication when it only uses one device?

[martin2345uk]

I am probably totally misunderstanding this but, this morning I went to sign in to my Apple account on my MBA using Chrome. For some reason it seemed to forget me, and I got a pop up saying a new device was trying to log in, enter the 6 digit code etc, but then the 6 digit code popped right up on the MBA, so I just typed that in and it let me in - what purpose does this serve?

 

[GTimG]

As I understand it, it prevents someone possesing your password from logging into your iCloud-Account without accessing your MBA.

 

[martin2345uk]

But if someone did steal my MBA they’d be able to get into my account..? 😬

 

[GTimG]

But then the person would still need your password, right?
If someone manages to steal your MBA AND your password, it is kind of hard to distinguish him from you for internet firms.