The most noticeable impact occurs when sending a large file from one user to another in the same office, while they are waiting for it.  This large file needs to traverse out to the Office 365 servers and back.  Now, realistically in most cases we are talking seconds here for this process.  Sometimes you can’t wait – when you need instant speed to collaborate on a document, we typically recommending using Lync and sharing screens for access in real-time.