Actually, a raised voice - used judiciously - conveys the urgency of a situation. As an example, if my own kids have been trained to obey commands uttered in a normal voice, then raising my voice lets them know that they are to obey immediately, without question and without delay.
Unfortunately, yelling tends to become a substitute for "making" the child obey. For a younger child, "making" them obey often means taking them by the hand and guiding them physically through the commanded actions. For an older child, "making" them obey often means ensuring that they do not enjoy life until they have complied - whether through punitive chores, removal of priveleges (my son hates it when I take away his computer priveleges), or similar.
But enough of my rambling...
I totally agree; a raised voice is important in urgent situations, like running out from between parked cars or avoiding a sharp object, etc. By "yelling", I was referring to parents who simply shout to vent their own frustrations, without any idea how ineffectual this makes them look and sound from the child's point of view.