To the original question, the advantage of the corner grounded delta as opposed to a totally ungrounded system is voltage stability to ground and better lightning resistance. In an ungrounded system transient voltages between any phase and ground are essentially indeterminate and limited only by the breakdown voltage of the insulation. Consider motors or transformers where the phases are enclosed in and wound on grounded metal equipment. More of a problem on older systems (and insulation materials) it can still present issues today. Corner grounding doesn't buy you anything operationally.
