Return on investment, better known as ROI, a key performance indicator (KPI) that's often used by businesses to determine profitability of an expenditure. It's exceptionally useful for measuring success over time and taking the guesswork out of making business decisions.  ROI defines (with real numbers) the success of each campaign and empowers you with data to help you steer your  campaigns in a forward direction. Knowing your ROI also places accountability on you to drive the company toward growth and not waste even one dollar.