Why some channels reward breadth and others require commitment

Budget allocation strategies often assume a diminishing returns model where the initial investment yields the highest productivity, with each subsequent dollar offering a lower return. This C-shaped response curve, resembling the top-left quarter of a circle, suggests spreading budgets across multiple channels to equalize marginal costs per acquisition (CPA) and maximize profit. However, some marketing channels exhibit an S-shaped response curve, characterized by an initial inefficient phase, an inflection point of steep growth, and eventual saturation. This S-shape fundamentally alters the optimal allocation strategy, rendering the common "test small, scale the winners" approach ineffective. The divergence in response curves, C-shaped versus S-shaped, impacts channel testing, measurement, and Marketing Mix Modeling (MMM) analysis. Google is increasingly integrating S-shaped campaign types, a trend expected to persist following its Google Marketing Live announcements. The critical distinction lies in how the marginal return, or the value of the next dollar spent, behaves. For a C-curve, this marginal return is highest from the outset, whereas for an S-curve, the initial dollars are the least efficient, with efficiency increasing significantly after an inflection point.