The problem here is that every nutrient line has different amounts and ratios of cal:mag, and there is ZERO agreement on the "perfect" ratio of cal to mag. Some say 8 to 1, some say 1 to 1, and honestly, you can get excellent results within those ranges depending on the other aspects of your grow-lighting, vpd, strain, etc. LED lighting really does increase the need for magnesium, but you can't just add calmag when you see a mag deficiency, because nothing locks out other nutrients quite so well as excess calcium. Another issue is, some of these bottled nutrients hardly have any cal/mg in them to begin with, instead the company tells you to buy calmag separate just to sell yet another bottle, so in that case, YES you need the calmag or some other form of cal & mg. This is why so many folks here use and recommend Jack's a/b, because it actually has everything you need in a two part formula. Even then, you still need to make adjustments for your individual conditions, for example, my tap water has around 40-50 ppm of calcium (likely carbonate) and my LED lighting and beloved OG strains both increase the need for magnesium. So, rather than just run Jack's a/b, I run close to Jack's 321 ratios, but reduce the calnit (to compensate for my tap water) and slightly increase the epsom salts. My point is, you can't make blanket statements like, "no one needs calmag" or whatever, because everyone is using different nutes and run different strains/lights, etc. In general though, if someone is running nutes that have an adequate amount of Ca to begin with, most likely they will just need epsom salts if they begin to see mg def, and adding more calmag will just make the problem worse. Yuck....sorry for the block of text lol