User blog comment:DanBing/December Vent Blog/@comment-8131762-20131205063324/@comment-7561418-20131206115050

When you're on visual mode you can't copy and paste (you can only paste, and it doesn't always work very well). But you can copy and paste on source mode.

Also, if you're trying to fix a mistake, it's easier to find it in souce mode.

But one thing I don't like about source mode is that there's no "undo" button.