If you have wondered, "How can I configure my Exchange environment so that cloud mailboxes can coexist with on-premises mailboxes?" the Exchange Server Deployment Assistant can be really helpful. You can walk through it and set various requirements, such as if you want all mail to pass through your on-premises server or if you want on-premises and cloud users to share calendar information, and it gives you a list of steps you need to complete. It's nice to play around with it a bit and get an idea of what you'll need to configure your environment for various scenarios.