The process of breaking down of dead organisms is called decomposition.
Decomposition allows nutrients to become free after organisms die and they are ready to be utilized by living plants and animals for their growth. My organisms which are part of the decomposition process are also part of the food chain. Without decomposition, nutrients would remain locked in the dead bodies of plants and animals and it would be very difficult for new life to grow. Most of the nutrients that are essential for the plants we get our food from, are the end result of decomposition.
This makes decomposition necessary for new life to flourish. Without decomposition life would practically cease to exist after one cycle.