Much to the chagrin of online retailers, customers typically do not make a purchase the first time they are on your website. (That would be too easy, right??) More importantly, customers who buy from your online store typically do not arrive on your website from the same traffic source every time. To emphasize this point, think about your own online buying behavior. If you’re thinking of making a purchase you may start out doing a 
few Google searches to see what’s out there. Then you may talk to a few friends to see what they know about the product. They you may do some more refined Google searches based on what you’ve learned so far. At this point you may find a few websites that sell the product and look reputable. Maybe you sign up for their email alerts to see if you can get a discount code or special deal. You receive a few promotional emails over the next few days or weeks and click through to the website a time or two but still don’t purchase. Perhaps you ‘Like’ their Facebook page to see if they are posting about any special promotions. Then maybe you talk to your friends some more. Then you do some research on the frontrunner companies to make sure they are reputable companies before you give them your credit card information. You do a few more Google searches to comparison shop. During one of those searches you see a Google Ad that catches your eye and you click on that ad. At this point you are in the buying mood and you decide to follow through with the purchase.
So in that sequence of events, which part of that process was the most important for the retailer? Unfortunately many retailers don’t know all this activity happened because they don’t have the right tools deployed on their website. If you use ecommerce tracking on your website you would know the purchase path described above contained organic search, email clickthroughs, social media clickthroughs, (those are called “assisted conversions”) and finally a PayPerClick ad closed the deal (this is the “last touch” attribute.) Some retailers have started to focus on the last touch attribute, assuming that is the most important part of their strategy because it was the one that closed the sale. Some have started to prematurely cut budgets on other funnels because they aren’t showing up as the last touch attribute often enough.
But I would argue the truth is that every part of that decision-making chain is equally important, and if you removed one of those links in the buying chain it is highly likely the purchase may not have taken place. If one of your competitors touched that customer with their social media or email message during the decision making process it’s probable you would have lost that sale. So while it’s important to understand how each of your traffic funnels are performing and always try to optimize each funnel, it is short-sighted to assume because a funnel isn’t sealing the deal as often as others that it is less important in the process.