Confluence has a build int attachments macro, which looks like this:
But it doesn’t tell which files are used in content. Sometime you can upload files by mistake or replace them with new ones.
If you are new to Confluence you might not even know that removing file from the view doesn't remove it from the page attachments! Especially users on Free instance can face this issue (Like it did!)
With Attachments Cleanup Assistant you can easily spot which attachments are not used and remove them with few click.