Question

why chemical coordination required although nervous system is prevalent in animals?

Answer 1

because if animals were using eletrical coordination,the nerve cell take some rest after sending a message.so animals use chemical coordination which the cells will not take any rest after sending messages.

Answer 2

Chemical coordination is required cuz not every action that takes place inside our body needs sudden stimulus.This can be best understood with respect to growth.Growth is the process that helps an organism grow in size and shape and also affects some of the behavioral characteristics.
As we know an infant dosent really few grow into a big human adult in few seconds or hours or even days.THIS PROCESSES OF GROWTH ACTUALLY TAKES YEARS TO HAPPEN.
our human body is very complex and every system,ranging from  a simple cell to the most developed organs like the brain,takes its own sweet time to grow fully.If such a complex system grows  really quickly, chances are that either they might not develop well or their functioning is not proper.This is something no one wants to happen ever.

Hence chemical coordination steps in here which is best suited for the slow but efficient growth of the diffrent parts of our body.