ATI 2012 and files synchronisation between local drives

Hi every body,
I just tried to use the new "synchronisation feature". But I am unable to understand how it works.
After creation of "New synchronisation" and selection of files to be synchronised :
- one file on the computer,
- the other on an external hard drive.
The file on the external drive was empty (destination file).
The analyse begin but the "destination file" remains empty and no files are duplicated from the computer to the destination file.
If somebody has additional informations I shall be glad to know.