An endorsement template defines how images will be Bates numbered (endorsed) as part of an export, as well as defining where native placeholders should be generated.
What's a native placeholder?
A native placeholder indicates that a single image (a “placeholder”) is included in the production, in lieu of an image-per-document-page. This image will retain a single number (e.g. Bates) representing the document.
This is desirable for content that is easier to review using a native application (e.g. .xls). In this situation, the native file is included in the export in addition to the placeholder (with a single number stamp).
Because native files will reveal content redacted on images, a native placeholder will never be generated for a redacted document. In this situation, a redacted .xls document will have each page individually imaged and numbers assigned.