Insects and birds are generally referred to as Uricotelic. This is the type of land animals, including arachnid(e.g; insects) and aves, which excrete nitrogenous waste in the form of uric acid. The process of elimination of uric acid after the de-amination of proteins, however, requires a lot of energy but has the following major advantages to the organism:- The thick white uric acid paste formed requires a very little amount of water, hence making this a very efficient elimination mechanism in terms of water preservation. This also helps the animal to reduce the amount of water required.
So, the correct option is 'Conserving body water'.