This paper demonstrates the impact of a specific campaign setup best practice — frequency capping — on media performance, highlighting potential cost savings from optimising this setting. Focusing on this single practice, we show how its implementation can improve efficiency and reduce media waste. Analysing thousands of campaigns across DV360 and Meta, we assess whether frequency capping was enabled (compliant/non-compliant) and examine its influence on media spend and reach. An optimised XGBoost model, trained via grid search and cross-validation, estimates media spend based on delivered results. Counterfactual simulations on 500 campaigns show that enabling frequency capping can decrease media spend by 27–38 per cent without negatively impacting outcomes.1 These findings underscore the value of frequency capping as a targeted, data-driven strategy for enhancing advertising efficiency and managing budgets effectively.