www.office.com/setup Blogs: Internet access is required to install and activate all Office 365 plans and to manage your subscription account. Internet connectivity is also required to access Office 365 cloud productivity services, including email, conferencing, IT management, and other services.
Many Office 365 plans also include the desktop version of Office, for example, Office 365 Business Premium and Office 365 Enterprise E3. One of the benefits of having the desktop version of Office applications is that you can work offline and have the confidence that the next time you connect to the Internet all your work will automatically sync, so you never have to worry about your documents being up to date. Your desktop version of Office is also automatically kept up to date and upgraded when you connect to the Internet, so you always have the latest tools to help you work. Compare Office 365 plans.
Also published on Medium.