Customers are going to engage with your business in many ways. Your full contact list is used for tracking all of the different interactions your have with customers and is very important to your business. You can track customers projects, sales, notes, emails sent, and content engagement. Because each customer engages in different ways, it's important to tag customers so you can identify their preferred communication method and connect with them in a way that works best for them! This also helps keep your email list clean as you only be sending emails to customers who expect them and interact with them.