What is the significance of the amount of urine output?

It reflects intake. The kidneys send out obligatory losses of 10-12 oz daily to remove your body chemical waste. But any extra liquid intake that the body needs will go out too. If you take nothing in a 24 hrs and become somewhat dehydrated, the output will be only 10 oz or so. Alternatively, in kidney failure the output may go down below intake level causing fluid build up in body that may need water pills rx.