Placement variants are essentially the available sizes for an artboard to be rendered out as the final creatives. Within a design, transform and other certain property edits that take place for a selected placement variant are saved to that particular placement variant and artboard.
Here is a full work through of how to use artboard placement variants:
Edit a placement variant
Click the canvas size button on the top pf the page to open the placement selector
Select a platform that you want to run your ads on
Select a placement variant (size) under the platform
Make edits on the elements in the selected placement variant
Clear edits of a placement variant
Select an edited placement variant.
Click Clear edits of current size button on the bottom of the placement selector panel.
Select placement variants in the Launcher
From the placement section in the launch settings, you are able to assign different sizes of the design you created in the Ad Builder to different placements.
Click on a placement option in the launcher
Select a size of design that fits the placement
Click Save to assign the selected size to this placement
The following properties of an element will be saved to the individual placement variant particularly:
Image mode (contain/cover)
Text size and line height
Text auto size mode