You can still print reports that exceed the paper size available from the print; however, only the leftmost portion of the report that fits on the paper is printed. Custom dimensions are used primarily for display reports viewed onscreen only.
Users who export reports to HTML pages may want to use this setting to control the number of “pages” included in each HTML file. The default behavior is to export each logical page to a single HTML file. For example, by adjusting the height of your page size to 33 inches, when exporting the report to an HTML file, it has the equivalent of three printed pages in the single HTML file. To ensure that all the pages in your report are contained in a single HTML file, set this height value to a large number.