http://johnalvino.com/the-real...ingle-leg-exercises/
My opinions come from power lifting for over 15 years, no injuries, great strength, flexibility, and speed improvements (I played in a professional soccer program, but the core work is great for baseball as well). Pick a muscle and a power lifter will have a much stronger muscle and body over someone doing lateral strength movements or swinging kettle bells (I do like some of the kettle bell exercises and the Romanian deadlifts - anything that builds explosive power will translate into explosive movements in sports. The guy in the article explains it much better than I can.
Power lifters and baseball players are two completely different animals. With that being said I have all my baseball players perform squat and deadlift variations. Nowhere in my reply did I negate the benefits of bilateral training. I just think it's extremely bold, and extremely wrong to claim that single leg training increases an athletes risk for injury.
Well designed programs will have a good balance between bilateral and unilateral work. Since we're on a baseball forum it should be noted that we need to incorporate movements and exercises in all 3 planes of motion. Baseball is a frontal/transverse plane dominated sport. You can squat, bench, and deadlift with baseball players all day but if they don't have any ability to move outside of the sagittal plane then you need to change some things in your program.