Not a must in my opinion but it can help you do all sorts of cool things.. Like adding crazy amounts of light or putting the lights closer without hurting the ladies and adding heat is less of a worry and less stress to ladies because they just continue on thriving. even after flipping on lights switches for example. Cannabis loves light.
"Respiration allows plants and other living things to release the energy stored in the chemical bonds of carbohydrates such as sugars made from carbon dioxide and water during photosynthesis. While a variety of carbohydrates, as well as proteins and lipids, may be broken down in respiration, glucose typically serves as the model molecule for demonstrating the process, which can be expressed as the following chemical formula:
C6H12O6 (glucose) + 6O2 (oxygen) --> 6CO2 (carbon dioxide) + 6H2O (water) + 32 ATP (energy)"