Why is it so important for animals to keep the concentration of their body fluids constant​

A balance of bodily fluids will prevent the development of diseases, the deterioration of body organs, and death of animals.

Explanation:

Water, blood, saliva, sweat and other body fluids should be kept constant and balanced through homeostasis because the sharp rise and fall of these fluids will prevent the organs of the body from operating optimally and this can lead to the development of diseases and consequent death. For example, water is a vital fluid. Too much of water in the system can lead to diseases like Edema where the legs begins to swell because there is no way of letting out body fluids from the body.

Too little water in the body can lead to dehydration and the increase in blood pressure because of the excessive concentration of solutes. The digestive and urinary systems have  mechanisms to keep this fluid under control.