When Download mode is set to Polite, the ad will download only the required script files to initialize the tag and prevents any workspace assets from loading until the publisher's page has completed loading.
A lightweight image is loaded to prevent overloading the main page. The lightweight image can be a default image or a dedicated preload image, which is a predefined blank image.
Please note that many publishers have "initial load" limits on their pages, and Sizmek Ad Suite (SAS) initialization scripts and pre-load image may count towards this limit. This limit is commonly set at 200 KB. Please check with your publishers to confirm what their limit is and what files qualify towards this limit.