I can think of two major important aspects of nutrient recycling. The first is that just like household recycling, it reduces the amount of raw materials needed for life. Reusing the same raw materials (in this case nutrients) over and over again requires harvesting fewer new raw materials for the same processes. The second aspect is that it helps maintain the cyclical food chain for all organisms on the planet. Microbes break down natural materials both organic and inorganic to provide nutrients for plants. Plants use these nutrients and gasses in the air to in turn provide nutrients to animals. And smaller animals provide the nutrients to larger animals. When the larger animals at the top of the food chain die their remains are broken down into gasses and raw organic and inorganic matter for the microbes in turn to start the whole process all over again.