Leslie, Why the Clicker?

Recently, Elletee asked why the clicker is used in training Leo, and I didn't know, though I know it's a popular training method for dogs. So, I emailed Leslie asking her "Why the clicker?" and this is her answer: 

I use the clicker to "Mark" the behavior from the dog that I like.  Because the clicker is exactly the same sound every time, the dog learns more quickly than if I used my voice and said "Good" for instance, when I see the desired behavior.  Our voices reflect so much: how we're feeling, how happy or sad we are, if we're patient or frustrated. NONE of which is relevant to Leo's efforts! The clicker communicates one simple message "You are doing the right thing!" and it doesn't include any of the multitude of overtones and undertones we convey with our voices.

Once the click sound is made I then move my hand to get the treat for Leo.  During the time that I'm reaching for and feeding him the treat, I also use my voice to convey my delight to Leo and my appreciation for his efforts! This verbal input becomes a bridge to the verbal praise he'll receive whenever he volunteers a desired behavior — and the clicker is no longer used.

The clicker is a training device only  and is phased out once Leo is good at the skill and repeats it easily. Then the skill is labeled verbally, and next, and the label is used AFTER Leo offers the behavior (in this way he can not fail!) and in the final step, the label "cue" is used to request the behavior and the reward is offered AFTER the behavior is elicited with the verbal cue. :)