Certain of the essential BCAAs can only be gotten from food, and the BCAA supplements are designed to make it easier to get those in your diet.
BCAAs are a well-researched supplement and generally safe for most people. BCAAs are not okay for everyone so consult your doctor before incorporating into your diet.
People choose to take BCAAs to grow muscle & enhance performance during exercise. Others take for potential weight loss benefits & exercise recovery.