Syncing comes in when two devices must reflect the same data. In case of Settings for Adobe CC apps, I would prefer to be able to choose "Put Settings" and "Get Settings". In that way it is easy to decide for yourself wether you are saving or restoring the Preferences.
In the case of Illustrator, Syncing did not do anything. I started my custom tunes Illustrator CC, chose Sync, quit, launched Illustrator CC 2014, chose Sync, and…. nothing. All units in pt, custom document sizes not available.