I used to sell clones, as a business. Buying them was a lot of fun and watching them grow. Now I only deal in seeds, not selling, just buying. There are clone only strains which are going around but I try to find those in s1 feminized seed format. I grow each seed like it's a potential newborn baby, i get great germ rates. If a particular seedling starts looking good, and turns out nice when it's in late veg, I will take a cutting before I flower the plant, which is what your friend is telling you. That cutting can be rooted, becoming a clone, then grown into a large plant, and then more cuttings taken from it, a whole lot of them at once, to have a fleet of clones of that particular strain, and run a crop of them. I don't grow big now so no crops but that's how it works.