I think the point that's being missed here by some is that if the runner at 3B takes off once the ball is hit down, she will arrive at home before the batter/runner reaches 1B. Further, if the ball is fielded by the infield, the sure out is at 1B and in the defender's mind, the runner at 3B doesn't have to go. Seeing her going or hearing she's going and the defender has to throw where she's less accustom to throwing upon fielding the ball. Given the runner at 3B will get home before the batter/runner will hit first base, the defender is under more pressure to throw quickly and accurately.
We've practiced this enough to prove to the defense and offense (batter and runners on 2B and 3B) that it's most often harder to get the runner out at home than the batter/runner at 1B.
On a grounder, the runners at 2B and 3B "GO!" If there are two outs, it's probably over anyway with an out at 1B. If there are less than two outs, odds of scoring are good, but if an out is made at home, you end up with runners at 2B (batter/runner advances all the way to 2B) and 3B--same situation to do it again.
I think the key here is getting the runners to TAKE OFF and run like hell the instant the ball is down. This is often the hardest part. Indecisiveness in the players in this play will lead to outs where outs shouldn't have happened.
What level of ball are you talking about? Listen, I'd rather have the pitcher have to look over at third and then hurry a throw to the first baseman who then has to throw home than have the pitcher throw right at home for the chance that something goes wrong. Same for a ball hit right to third. It's a dumb strategy that may work from time to time. I want the runner to read the ball past the pitcher and decide on how hard it is hit and then go, or alternatively be told to go automatically when hit to the middle infielders.