Agree with Steve Yao. These are the different products and you can buy them separetly. The advantages both products together are:
1. You will have Office licenses (Word, Excel, OneDrive ...)
2. Easy to integrate Dynamics 365 with exchange
3. You can set up integration with SharePoint (depend on Office plan)
4. Integration with Office 365 groups
5. Integration with PowerApps
6. Integration with PowerBI
7. Integration with Flow(Power Automate)
8. You can use Teams for easy collaboration in company