1. Knowledge worker productivity gain
Office 365 provides many tools for increased productivity in SharePoint, Lync, and Office Professional. Features in Lync Online that contribute to productivity gains include Presence, IM, and unified communications. For SharePoint Online, there are easier collaboration and document search/retrieval. Outlook was especially important for productivity gains in Office Professional.
Increasing to a 25 GB mailbox will save users time from having to regularly delete items to free up space. In addition to consuming time, this activity is also a source of annoyance for users. Users also see productivity gains from features such as scheduling assistant and conversation view.