Anaerobic metabolism is less efficient than oxidative metabolism.

A single glucose molecule generates only 2 ATP molecules while being metabolized to 2 pyruvate molecules via anaerobic glycolysis. Oxidative metabolism of the pyruvates via the tricarboxylic acid cycle yields 34 ATP.

Even though less efficient, anaerobic metabolism is sometimes an important temporary supplement for the production of energy molecules. This is needed for intense exercise such as an antelope running from a lion. A short but intense burst of energy is needed. Efficiency is not important.