I thought it was the opposite

I read an artical by a well known gardener, the first thing that I came across was about Pelargonium, where he said he doesn't feed them, yet I have always thought Pelargoniums were gross feeders. The second was about legumes, advising planting  brassica after them as they add nitrogen to the soil, again not what I thought actually happens, I thought that the plant used up all the nitrogen producing peas or beans and if you wanted nitrogen you had to dig the plant in before it started to produce a crop
So have I got it wrong with the two of them?