I was under the impression in WWDC16 it was anounced that exporting developer profiles from one machine to another was no longer neccesary and XCode (8.n)managed everything now.
However, in the Apple documentation here https://developer.apple.com/library/content/documentation/IDEs/Conceptual/AppDistributionGuide/MaintainingCertificates/MaintainingCertificates.html it states:
If you want to code sign your app using another Mac, you export your
developer profile on the Mac you used to create your certificates and
import it on the other Mac.
(talking about the signing identity) "If the private key is lost,
you'll have to create an entirely new identify to sign code"
This is out of date. Xcode 8 will generate a new identity for you on another Mac.