Now if you are going for mass, you need that post workout shake to increase insulin release, activating channels, carrying in aminos acids...blah, blah, blah. But you body will do that anyway, the difference, it will use your own fat as the source of fuel...and you probably have enough amino acids floating around.
Do you need that post workout shake if your going for mass gain? Since spikiing insulin decreases HGH levels does expediting and maximizing the amino acid strorage in your muscle pwo outweigh decreasing your HGH levels at the time when increased HGH levels are extreamly beneficial? Don't know the anser to this one, just throwing it out there (I have been struggling with this question for a while).