The Layout Placeholders area of the Working Illustration is where you can rearrange the display order of your plots without having to generate the actual large plots. Each plot is symbolized by a small test-tube icon "placeholder." This is useful when working with large or many FCS files. Within Layout Placeholders, you can click and drag column or row headings to change their display order. Once you have finished rearranging your figure in layout placeholder mode, you can click on the Illustration tab to see the corresponding plots. Be sure to click "Update Dimensions" after making changes in Layout Placeholders.

You can see Layout Placeholders in action in a tutorial video. (It's the last step for that section of the tutorial.)