We have a new directory in place; we can start adding users and assigning them access rights. But there is a good chance that we already have an identity solution in an on-premises environment and that users already have one identity in place. Providing users with an additional identity can cause issues and confusion. Users will have problems detecting when to use which account, and if the same or a similar account is created, users will start typing in the password for the wrong account...
Fortunately, with AAD, we can use Azure AD Connect, and that will allow us to sync accounts from on-premises AD to Azure and allow users to use the same account for everything. This will make things easier for everyone; users will not have to think about which account they will use (as it's the same account) and admins will have less issues to resolve...