Sync has nothing to do with slaving to your telescope. Sync (like a telescope sync) allows you to correct the angle that your dome is reporting. For instance if your dome is pointed due north (0 degrees) but is reporting 30 degrees, you can use "Sync" and input 0 to correct this. The dome will then be synced to 0 degrees at its current position.
Not all mounts support this, and you probably don't need this behavior unless your dome isn't pointing where it should be pointing.
Thanks,
Jared