Perhaps most controversially, the report states that the government believes it can “persistently” track the phones of “millions of Americans” without a warrant, so long as it pays for the information. Were the government to simply demand access to a device's location instead, it would be considered a Fourth Amendment “search” and would require a judge's sign-off. But because companies are willing to sell the information—not only to the US government but to other companies as well—the government considers it “publicly available” and therefore asserts that it “can purchase it.”
Basically, they're buying the profiles corporations already have on you. It isn't just to sell you pasta sauce; your shoppers' card also helps build a government profile on you.