I wouldn't recommend using that method. It won't consider images being referenced in either category/document or product descriptions. Those images will likely be considered orphaned and get removed. The module I will put together, hopefully in March will address embeded images as well as those directly associated with products/categories etc.
In theory, filemanager contains all images found in the /images/source directory regardless of if it's in use in the store, so your process isn't really removing orphaned files. It's likely removing images which are not in sync with the store DB. yo