This enables you to make a graphical presentation of all your projects over time or just a subset of your projects whatever you prefer. Next to the normal functionality of the timeline what is now available in Project Web Access you have the added ability to add projects to the timeline. Project Online is still in the preview version this is not the final product so changes can still be made. However there is a little more in Project Online. I personally really like this addition to Project Web Access as it gives you a nice graphical presentation of your project. That post you can find here and this post is a little addition as Project Online has the Timeline in Project Web Access. Previously made a post about the Project Professional Timeline and how you can use it.
For people that do not know what Project Online is, it is basically Project Server 2013 in the cloud. With the Project Preview that started in July I had the time to test out Project Online.