What I would understand by syncing is something like Dreamweaver has built in. You configure an ftp directory on a remote server and tell it where its local equivalent should be. You then download everything and the direcotries remain storngly linked. ie you make a change in subdirectory A and it will know that it uploads to subdir A on the server without you needing to do the usual thing of changing to the local directory with the new file, changing to the remote directory you want it to go into and then clicking and dragging. It does much more clever things. I'm not sure if I've explained it will but it makes it vastly easier not to make a mistake when you are dealing with keeping a local copy of a website synced with the server copy.

I've yet to find a client outside a big product that does this though which is why I occasionally have macromedia stuff installed on my computer.