On Sunday night, the enormous drugstore company CVS said it had agreed to buy the enormous health-insurance company Aetna for almost $70 billion. It’s a deal that, if government regulators and both companies’ shareholders give it their blessing, would be the biggest deal in the U.S. this year. There are two main reasons CVS would benefit from acquiring a health insurer—one that’s specific to the economics of the health-care industry, and one that applies to just about any company that is trying to make money at brick-and-mortar stores in 2017. First, if CVS does buy Aetna, it might be able to win over more business—both from individual consumers and from employers buying plans on behalf of their workers. In theory, that’s because CVS could gain a competitive edge by reducing the cost of providing care to Aetna’s customers. How could it do this? CVS is not just drugstores. In 2006, it acquired a company called MinuteClinic, which operates walk-in clinics. CVS now has more than 1,000 of them, including in its stores and also in some Target locations. This is one of the main reasons CVS and Aetna could, together, save money: A company that sells insurance could start providing care directly, and steer customers not immediately to doctors but rather first to its own ensemble of nurses and pharmacists working at CVS locations. An example illustrates why this could be powerful: If an Aetna customer has diabetes, it can be extremely costly (for both Aetna and the customer) for them to frequently see doctors for help managing their condition. Instead, a merged CVS-Aetna could encourage this customer to go to its walk-in clinics regularly for check-ins, potentially limiting those higher-cost doctor visits. A similarly salutary outcome could arise from having patients with other chronic conditions visit these clinics, perhaps to make sure they’re taking their medication—because when they aren’t, their conditions could worsen and they are likelier to need to see a doctor. In this way, CVS-Aetna could reduce the cost of the care it provides, perhaps prompting competitors to lower their prices in response. The second reason CVS might see an advantage in buying Aetna is a