People need kidneys because the kidney filters the waste substance out of your blood and balances the levels of salt and water, when your body has taken the nutrients from food some of the of the waste products are sent back to your blood, so your kidney will filter continuously so that your blood will not contain the waste substances, in general your kidney is a "Filter/Cleaning Staion" for your blood, if you didn't have kidneys the waste products will build up in the blood and severely damage your body, the other functions that your kidney does is balance volume of fluids and minerals in your body. The substances that have been filtered form your kidney are mixed with water and are transformed into urine ( Pee ). Kidneys also produce Vitamin D and help regulate your blood pressure and the simulate the production of red bloods cells so in conclusion the importance of the kidney is very important.
