I got the answer to that first question.
Plants utilize PPF and PPF changes with color temperature. Different wavelengths excite photosynthesis in different levels. Here is a widely accepted graph for understanding this. McCree's relative quantum efficiency curve;
Red bands induce more photosynthesis than any other band as you can see. But plants react to both red-green-blue bands with photosynthesis. The problem is, some bands are just more efficient, or they just seem to.
Red dominant wavelength composition will result in the biggest bio-mass, which includes every part from root to top weight of a plant. Leaves and stems are also included. If you are growing this type of plant, then you need to use monochromatic LED's, 15W of blue with 85W of red in each 100W.
Blue dominant wavelength composition will result in better root system and higher quality products compared to red. If you are after a top shelf product, then you should roughly use 15W of monochromatic red and 85W of polychromatic full-spectrum LED's. The recipe is not %100 precise but these combinations of wavelengths are also widely accepted among manufacturers. Blue is just as important as red. You can observe the quality difference in cannabis and tomatoes clearly. Tomatoes don't get swollen and cannabis get higher rates of cannabinoids and terpenes when you use enough blue.
Green dominant wavelength composition will result in lower photosynthesis rate but if you provide your plants with lets say %25 blue %25 red and %50 green, they will still grow great and give amazing products. Green penetrates into the canopy and therefore doesn't induce photosynthesis just as efficient as red or blue. That is why nobody uses a green dominant spectrum. However, having green band in your composition has amazing benefits if the percentage is kept at a reasonable level. %25 green can replace %25 blue without affecting the biomass produced. Same thing doesn't apply with red but you will be needing green or blue to get a proper root system on your cannabis plants.
About auto-flowers and fast veg. clones for SOG, I don't think it is a good idea to boost red too much. Quality decreases after some point due to lack of blue. Also these kind of plants need to establish a good root system in short time so giving them too much red might end up in smaller bio-mass.
About long vegging properly trained plants, it will make a great sense to use too much red in late veg. to promote stretch and get a longer node separation to properly do a SCROG or whatever you are doing. Some trains like my Pink Kush(Barney's) have a very narrow node separation. I couldn't get amazing results when I trained this plant so I had two options. Adding a red boost for the stretch on late veg. or go SOG with lots of small sized clones. I chose the SOG way and can't be more happy with my garden. Keeping things minimal always paid off for me.
The best alternative in my book is to use a well balanced spectrum in all phases. That's why I customized my own LED fixtures around 3900K, which I believe is very near to the sweet spot for cannabis cultivation, as well as many other plants. I will built tunable white fixtures this year and have total control over the stretch. That will be the ultimate grow light I think.
Hope these help. Cheers