ROI is a finance concept which is under-applied in the marketing world.

Money you spend on marketing should return more in profits (not just sales) than what you spend on it.

There are two reasons it's often a neglected concept:

1. It can be difficult to measure. For example, how do you determine ROI for a billboard, when it is just part of your marketing mix?

2. Incompetent marketers discourage metrics by exaggerating the problems of #1.

Yet there is no path to long-term growth and prosperity for a business, that doesn't involve cost-effective marketing, good product or service quality and smooth customer service and delivery.