You'll find different reasoning for it. But my personal reason is because I strictly run autos. Which means about a whopping 2 weeks of veg time. Lol. Most autos show sex/preflower from day 17-21. From there, they are in preflower/flower mode for the rest of their pre programmed life. Photos.. Well, you veg them as long as you want to, so the grow nutes may come in handy there.. For autos its basically either 4-2-6 NPK (grow a/b) or 5-4-8 NPK (bloom a/b). They both have the same core indredients and if you only use one you can always add a simple booster for the part you didnt buy. I like the blooms ratio better and my soil will always start with enough nutrients to get the plant through its first 14-21 days of "growth". So "grow" nutes seem kinda pointless to me with autos. And yes, they also make the products just to sell to unknowing people like myself. For instance, bud candy the same thing as carboload. Same. Thing. But they will still sell you both. I fell for it and bought both. Lol. But I think the grow/bloom difference comes into play more so when photos are involved.