Hydro definitely makes it easier to control experiments, especially with DIY hydro nutes.
A tool like hydrobuddy makes it very easy to see what adding a gram of calcium nitrate will do to ppm Ca and N, for example. It's useful for keeping P within the 30-60ppm range, and keeping a proper/controlled K:Ca:Mg ratio.
I've experimented with different levels of iron, manganese, boron, etc. I try to keep iron toward the high side (5ppm), which I think really helps with high intensity light to prevent bleaching. (i've never had leds turn my tops white from too much intensity, only brown/black)