Advertising
Audience saturation
The point at which additional budget mostly buys more impressions to people already reached, rather than new people.
What makes it wrong.
The mechanism, not the warning.
Saturation is often misread as creative fatigue, and the two have opposite fixes. Fatigue is solved by new creative into the same audience; saturation is solved by a larger audience for the same creative. Frequency against reach separates them.
In detail.
Saturation is visible before it is expensive: reach flattens while impressions keep rising, so frequency climbs and response falls. It is a property of the audience size relative to the budget, not of the creative.
It is the reason a campaign that scaled well suddenly stops scaling at a particular daily budget.