This is a cool feature that improves the user experience when generating preview reports on a lot of data. Until v2008.3, XtraReports used to generate the entire report before showing it to the end-user, and, in those cases when there was a lot of data to report on, this could take an appreciable amount of time and leave the user with an unresponsive program as the preview was being created.
In the new XtraReports, there's an option to generate the first page of the report preview as before and display it immediately. Meanwhile another thread continues to generate the second and subsequent pages in the background. This gives the user control of the report and the program so that they can view it and page through it as normal. As the second thread produces pages to view, they become available to the end user.
Here's a screenshot from the demo program showing this in action (the final report is over 2000 pages long).
