There are almost 70 Roles in Azure AD and nearly 12 roles in Exchange. Each of the roles allows people in your organization to perform specific tasks in the admin center. Allowing the people with the certain roles will help people to manage their work in the organization efficiently. For example, A user in an organization is assigned with the roles of Exchange Administrator. If any of the user face the issue related to exchange, then he/she do not have go directly to the Global Administrator to solve the case rather they can go to the Exchange Administrator.
To know more about role assignments click on the link below:
About admin roles in the Microsoft 365 admin center - Microsoft 365 admin | Microsoft Docs