right [/sarcasm]
what is the supposed benefit of omitting the grow from the standard GH mix?
The three part GH system has you applying nutes in too high a concentration, and dumping your rez often.
At the end of the day, what you are concerned about is making it simple and minimizing costs to the grower and reducing waste. Given that GH Bloom and GH Micro have all of the nutrients that are otherwise also covered again in GH Grow, it doesn't make sense to buy a third product when you have those nutrients covered already by using just GH Micro and GH Bloom, applied in a proper ratio depending on the stage of the grow you are in.
Put another way, there is a *lot* of nitrogen in GH Micro. So much that you don't need GH Grow to get that nitrogen in the quantities your plants need. You can just rely upon GH Micro instead. You end up using more GH Micro using the Lucas Ratio than you would in a three part application - but the benefit is that you use ZERO GH Grow. In the end, having to buy and use one less product means a cheaper and simpler fertilizer system.