I myself wouldn't compare it to using steroids, but rather look at it as one more tool in the arsenal to stay anabolic and keep those muscles growing.
If you have everything nailed down as far as an effective lifting program, rest, and nutrition, then anything else in supplementation is taking these areas to another level.
BCAA's main purpose is to buttress keeping amino acids flowing in your body during intense training and at other times throughout the day.
Look at it this way if you go into the gym and annihilate your chest muscles causing micro tears in the muscle fiber and then go all day without eating you are going to be in a very catabolic (muscle wasting) state. You aren't giving your muscles any nutrients and building blocks to repair the damage done to them.
Protein, carbs, and fats, are the nutrients needed to facilitate repair and growth. BCAA's are the building blocks of protein essential amino acids that your body must get from the food you eat are from supplementation.
BCAA's taken around training and through the day provided all other bases are covered will ensure one staying anabolic (muscles growing) and ward off being catabolic (muscle wasting).
If one was a natural lifter they would be a benefit and could increase muscle gain as well as if one were on steroids. Remember, any one who lifts with the goal of gaining muscle= bodybuilding and getting significantly bigger and stronger wants to have every tool available to help one achieve this.
BCAA's are another powerful tool to be used synergistically with your whole nutritional plan to achieve this .