Marketing Cloud, Trailhead...
Does my business need a CRM system?
1. You have no single source for customer information.
Does your company have customer and order information in more than one location? If the answer to that question is “yes”, then that's one glaring reason why a crm is required.
If you have customer details in spreadsheets (or sticky notes), then your sales team — and everyone else who interacts with your customers — is at a disadvantage. When information changes in one system, it isn't automatically updated in the others. There's no complete, single view of every customer’s contact info, orders, and interactions.