WD Sync will sync both locally and remotely. When your PC is connected to the local network WD Sync will sync through the local network. When connected to network at some other location WD Sync will use the internet to connect to your My Cloud and sync. See the following links. The User Manual explains WD Sync in Chapter 4, Backing Up and Retrieving Files, Synchronizing Your Files and Folders with WD Sync.
My Cloud User Manual: http://www.wdc.com/wdproducts/library/?id=439&type=25
How To Setup & Use WD Sync: http://mycloud.com/learn/?id=mycloud#wdsync
Please note that syncing files is different then backing up files. Syncing and backing up are two different tasks that accomplish slightly different end goals.
Also, before installing WD Sync perform a forum search to read the various issues/problems people are having with WD Sync. For local syncing some are dumping WD Sync due to the various problems with it and using Free File Sync (http://www.freefilesync.org/). Note however that Free File Sync doesn’t support syncing remotely other than using SFTP. The My Cloud does not officially support SFTP at this time.
