Let's talk BCAAs.
Do you need to take them in supplement form?
Short answer: No.
BCAAs are readily available in many of the protein sources most of us are already eating. Your body will only draw on BCAAs for fuel during exercise IF you're NOT eating enough or taking in enough carb.
IF you are properly fueling before and during exercise, and the rest of your day, you are easily getting all the BCAAs you need.
For example, each of the following foods contain ALL the BCAAs you would need daily to prevent protein breakdown during aerobic exercise:
3 oz water packed tuna.
3 oz chicken.
1 cup nonfat yogurt.
1 cook cooked beans/legumes.
Dairy products and whey protein are great ways to replace BCAAs as well. Getting BCAAs from whole food sources vs. supplements also allows your body the ability to absorb them better. There are substances within foods called "food factors" that help with absorption in ways that cannot be replicated by supplements.
BCAA supplements can be expensive and large amounts of BCAAs in supplement form on a daily basis, can actually interfere with the absorption and balance of other amino acids. BCAAs in large amounts can also cause stomach upset, and there is research indicating high intake of BCAAs with increased diabetes risk, impaired fasting glucose, and insulin resistance.
If you were to choose to supplement with BCAAs it would be wise to choose a protein supplement that contains a full array of amino acids (and thus, you might as well save your money and just eat whole protein sources).
If you still want to supplement (running it by a doc first is always) recommendations indicate BCAAs should be taken either during training and/or hourly with an electrolyte solution before and during prolonged exercise (recs based on studies showing BCAAs increase marathon performance by 4%, may decrease mental fatigue during exercise, and may decrease muscle breakdown). Taking them at any other time, like before bed, would be a waste of money and could even interfere with sleep as BCAAs decrease serotonin and inhibit the uptake of Tryptophan and Tyrosine.