During this video Matthew Sweezey provides a clear example of when ROI should be used to measure marketing success. ROI is for focusing on campaigns that begin with a cash spend and finish with a closed monetary deal. The calculation is easy. 

However, lead nurturing, sales support, email and most other campaigns do not start and finish with a monetary value, although still extremely important. These should be valued with Velocity and Efficiency. Watch the 90 second video to understand why these two metrics are important measures.