During normal operation, this page will not render its underlying content until it's absolutely needed for display or printing. Once it does, however, the rendered content will be cached internally for quick access in the case it is needed again.

There are situations where this behavior is not desired and where this method can help. For example, if you are looping through all pages of a document to print them, each page need only be accessed for a short period of time, after which it is no longer needed. However, because each page will cache its rendered content, the processes memory will continue to grow as each page is printed and will only be released when the parent document is no longer referenced. If the sheet is very large, all the memory of the process could be exhausted while the pages are still being accessed.

Calling this method after accessing a page for display or printing will release the internal reference to the rendered content. The rendered content will be recreated later if it is needed.

This method has no effect on an instance created by the Clone method. A cloned instance has no connection to the original spreadsheet data, thus cannot regenerate the rendered content were it to be cleared.

Reference