Budgeting & pacing
Diminishing returns
Diminishing returns describes the point at which additional spend on a channel, audience or tactic produces progressively less outcome per pound, as the most responsive people are already reached and auctions push into more expensive inventory. It defines the practical ceiling of an allocation.
In practice
Every line has a response curve. Early spend buys the cheapest, most receptive attention; later spend buys repetition and marginal audiences at rising cost.
Recognising the curve is what separates reallocation from momentum. When marginal CPA on a winning line crosses the marginal CPA available elsewhere, the next pound belongs elsewhere.