Since the time the classic B2B sales funnel was developed in the late 19th century, over many decades it has gone through a lot of changes. Today due to digitization of world B2B sales funnel has a different approach in its 5 stage model. But the basis of the B2B sales funnel remains the same. It is a great way to analyze at which point you are losing your customers and figure out the best way to grab those lost customers back into your business. According to this model, the value of the potential customers or leads keeps increasing the further they go into the funnel.
http://www.dqmpro.com/blog/b2b-marketing/understanding-the-b2b-sales-funnel/