When you choose not to opt out of the research component when you first sign up for AncestryDNA, your DNA results as well as your public family tree are used as data for scientific research. Although this can include the use of your results by third party companies with associations with AncestryDNA, it is also used for projects like the new article that has published in Nature Communications. This article examines recent migrations within the United States and reveals ethnic clusters that are supported by DNA data.
You can read about the research on the Ancestry Blog:
Nature Communications publishes AncestryDNA breakthrough on genetic communities
You can read the open access article in Nature Communications:
Clustering of 700,000 genomes reveals post-colonial population structure of North America