This feature is for marketing professionals who want to fully understand the impact of email marketing in the conversion process.
Right now, when you look at email marketing reports and review the deals influenced, you will see that these deals are tagged only when the customer opens and clicks the email. However, there are also cases when a customer who is brand aware will open the email and go directly to a browser, and can eventually decide to buy. (As a returned brand user for the many marketing emails a customer receives, there are times when a user receives an email, opens it, and navigates to his/her own browser to type in the website too.)
I think Hubspot should give its users the intelligence to see these two types of attribution.