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.
For instructions on generating publicly accessible links see Sharing files and folders via Dropbox and Sharing files and folders via Google Drive