Image transformation is a tool for adding custom designs and filters to product images, i.e.: Facebook's Dynamic ads.
The design is added directly to the product feed, and can therefore take into account the feed's information and be made "intelligent".
Facebook ads are pay per view, so it's about grabbing every chance to show your value (both directly through sales and indirectly through branding). Also it’s easy to disappear in the crowd if you aren't competing effectively, since more and more companies are using custom designs.