You don't need to be online to use OfficeSuite apps after they are installed and activated on your devices. However, you will need internet access initially to install and activate OfficeSuite, to install any updates, and to manage your billing. Internet access is also required to access documents stored on MobiDrive, unless you install the MobiDrive desktop app. However, after your OfficeSuite apps (like Documents, Sheets and Slides) are installed, you can use them offline.
You should connect to the internet regularly to keep your apps up to date and benefit from automatic upgrades.