Used for: removing duplicate values from a list.
If you have a field containing a list of values, you can use the "remove duplicates" rule to delete duplicate values if present. This could be useful, for example, when you have a list of images with duplicate images in there. This example is shown in the rule below:
Which results in the output below. The original list of images has a duplicate image link, the "deduplicate list" rule takes care of this as you can see in the field "images_without_duplicates".