This short video briefly explains about the benefits of using the Projectum Timephased App for Project Online/Server 2013.
The main purpose of this app is to allow users of Microsoft Project to timephase financial information, without creating too many custom fields as this impacts performance.
The app is expected to be released in the marketplace beginning of September 2013. However, a trial version is already available for download but doesnt allow user to sync data back to Project level custom fields. In this case you would need the pro version.