This tactic can be used against Terran players especially because in TvT there is race about making more Tanks.But if you build fast Wraith to make a surprise assault to your opponent it will really give you lots of advantages and maybe you will win the game easily.The main function of Wraith is damaging the rival’s economics by killing Scvs.The cloaked Wraith can harm anything and if they are outnumbered they can explode Turrets easily which will create the path of the victory.Here the important point is making wraith secretly and fastly.Which means high amount of vespene gas and mineral flow and also defensive position at the very early stages of the game.So you must calculate these parameters to try this tactic effectively.