There is next to no science or studies that I know of to back up my own personal experience, but I had some pretty solid results essentially consuming large amounts(150-175g)of BCAAs a day between meals. I didn’t change my diet, but between meals I would have 25g or so of BCAAs. I’d also drink between 30-60g before, during, and after workouts. I got a lot stronger during this period, I also leaned out without changing anything in my diet, though this could just be attributed to being able to preform at a higher level because my recovery was through the roof.
I did this quite awhile ago, and stopped because it was getting a little expensive. And because I used plain BCAAs mixed with natural flavorings, and that got old very fast. There are better and cheaper products out there now, so I might try it again at some point. A month shouldn’t be too painful on the palate or pocket book now days.
As for the OP’s original question, no, I don’t think BCAA’s are necessary. Very little if any supplement would I call “necessary”, but that doesn’t mean they are very beneficial.