Well, for one, the riskless rate of return could raise above zero, and you might have to factor in the amount of risk your ad buy represents. If you advertise i

Well, for one, the riskless rate of return could raise above zero, and you might have to factor in the amount of risk your ad buy represents. If you advertise in order to grow your user base, but that userbase is neutral or net negative, when funding costs go up, your gamble that you can shift customers from neutral to profitable is less viable. But imagine a secondary structure of ad buys: you buy mobile ads promoting your app, which monetizes itself through ads. If the ad market falls, you've effectively bought ads high and sold them low.