What are BCAA's?
Branched-chain amino acids are essential nutrients that the body obtains from proteins found in food, especially meat, dairy products, and legumes. They include leucine, isoleucine, and valine. Branched-chain amino acids stimulate the building of protein in muscle and possibly reduce muscle breakdown. Aside from food, you most likely have seen people drinking or taking BCAA pills.
What Are the Benefits of BCAAs?
Many bodybuilding sites recommend supplementing BCAAs, saying it is extremely key for muscle hypertrophy (the growth and increase of the size of muscle cells). Others claim it will help athletes improve their performance by fueling their exercise, sparing glycogen, increasing protein synthesis, reducing protein loss during exercise, reducing muscle soreness, reducing fatigue, and improving immune function. Yet there is a lack of evidence to support these claims.
Although there is a lack of evidence, there is no hurt in taking extra BCAAs in hopes of gaining an edge (minus the extra calories if you're trying to cut). But don't excpect them to give you super powers.
I'm sure you've seen people walking around with jugs of colorful water, most likely with BCAAs in them. Maybe you are one of those people. No judgement.
As your workout drags, BCAA levels get depleted and you get tired. So drinking them while you workout may help keep your energy up. Note, this is usually for longer workouts, not necessarily weight lifting where you're only in the gym for 1-2 hours.
A More Practical View
BCAAs play an important role in muscle building process, but you can obtain all the necessary BCAAs in regular foods. For example, 3-4 oz. of chicken breast contains the equivalent of a daily supplemental dose of branched chain amino acids (100 g chicken breast: 470 mg of valine, 650 mg leucine, and 375 mg isoleucine) while a quarter cup of peanuts contains an even a greater concentration of BCAA’s. BCAAs are effective and useful, but adding an extra 10 -15 grams on top of your diet won't benefit you in any noticeable way. Even research that supports the use of BCAAs have found little change from supplementing.
OVERALL
For most people starting out, you don't need to supplement BCAAs. Focus getting 0.8-1.0 grams of protein per pound of body weight from your food on a daily basis and you won't need to spend extra money for a colorful BCAA drink.
Sources:
https://www.webmd.com/vitamins/ai/ingredientmono-1005/branched-chain-amino-acids