I would imagine that there would be some increase in CPU usage for Explorer as CoreSync tries to establish a connection with servers (via Operating System) and does the hand-shake. There are a few other things which happen in the background around validating authenticity etc. But after this initial chatter, the CPU usage for Explorer should settle down.
I would be interested in knowing more on what happens, say after 10 minutes of re-starting the Sync. Thanks much.