Explanation of the git annex sync --content . command

Question

While reading one of the articles, I found the following: $ git annex sync --content

But I don't understand what the author meant here: "If someone else has shared assets to the server and you need to pull them, git annex sync will prompt your local checkout to pull assets that are not present on your machine, but that exist on the server."

My question is can you explain what is meant here "will prompt your local checkout to pull assets"?