Data vs. Sync?

[ellje]

Excuse my newness to android, buying having a difficult time determining the difference between the data and auto sync toggles. I've had my auto sync toggled off, but data toggled on and my gchat and email seem to update regularly. Would auto sync use less battery to get the same result?

 

[ellje]

hmm... Turned Data off this morning, and I can't even connect to gchat. Seems that I have no network data capability at all with this toggled off.

I still have no idea what Auto-Sync does, as even with it toggled off my Chat and Email Apps update instantly. I feel as though I'm missing the big white elephant in the room, here...