Many people only test to get ethnicity results. That's their prerogative.
I love finding relatives all over the globe and am lucky to have "met" both in person and virtually, some lovely new cousins and like-minded friends through both paper and genetic genealogy.
I certainly don't have a hope of understanding the technicalities of how it's done but the genetic genealogy experts say ethnicity estimates are just that, estimates.
I think of it as an extra, interesting and even fun addition to my DNA matching for genealogy but I don't take it as gospel even though the results are pretty much what I would have expected from my years of research.
Given that quite a lot of that research has been confirmed through DNA matches I am in agreeance with their "estimates" and find not all that much difference between the results of the companies I have uploaded to.
This is my initial AncestryDNA ethnicity results breakdown and the map.
Below is my newly updated breakdown estimate and map:
There are also explanations available.
You can read further AncestryDNA FAQs about the updates HERE
And more in-depth information on updated ethnicities by Debbie Kennett at Cruwys news Blog.