You can attach files to pages if you want the files to be associated with a particular page. This means that when you are moving and copying pages, the attachments are copied together with the pages. Also, pages on your site can be set up so that they can show files, usually images, attached to particular pages.
Page attachments
Note that page attachments can be stored in the database and/or file system based on the system settings. Learn more in Storing files.