The cool thing about BCAAs is that they are either used directly to build muscle or to provide energy. The liver doesn't decide to send them to other functions in the body.
BCAAs have also been shown to blunt the catabolic hormone Cortisol. Lower cortisol means higher testosterone.
BCAAs also enhance recovery decreasing delayed-onset muscle soreness.
The typical recommendation is to take 5-10g with a whey shake in the morning, pre-workout, and post-workout. Although some like to drink them all day. Others drink a BCAA drink intra-workout to keep their energy levels high while training.