Here the law is your rear wheels have to remain behind the stop line while waiting to turn left. The intersection has to remain clear of stationary vehicles.This can sometimes be dangerous.
If you are in the intersection waiting and your light turns red, you begin your turn, people continue through the light that just turned red, most times speeding to get through the yellow light they just missed, you get T-boned as you turn. I've seen it more than once.
Also as you are sitting there with your light now red, you are congesting traffic in the opposite direction.
I could be wrong on this point, but I believe it is illegal in some states.