The practice of closed-loop marketing is to be able to execute, track, and show how marketing efforts have affected the company's growth. An example of this would be tracking a website visitor who becomes a lead down to the last touchpoint when they close out as a customer.
When done right, it's clear how much of your marketing investment has led to new business growth. One of the biggest business benefits of implementing an inbound marketing strategy and using inbound marketing software is the ability to do closed-loop marketing.