If you click Yes , the items in the template, including any changes, will be available to all documents to which the template ...

If you click Yes, the items in the template, including any changes, will be available to all documents to which the template is attached. If you click No, the changes will be discarded from the template. If you do not think you made changes to the template, be cautious about saving it, because potentially malicious macros can be distributed in this way.