Attaching a Link as a Brand Asset is a powerful way of saving time. Instead of uploading files one by one, you can instead link to a Folder that has a bunch of files in it.
For example, if you have various versions of your logo. Rather than upload each logo as an Asset you could instead link to a Google Drive or Dropbox folder that has all your logos in it.
However it's important that when attaching a link that it is set to be Publicly Accessible without needing to log in to access the file or folder.