Testing Testing 123, Why?

Many times people will step up to a microphone, tap it a few times, clear their throat, and then say, "Ahhhm...Testing? Testing? 1,2,3?" It is usually stated in the form of a question, as if the person themselves cannot hear what is going on, and needs to ask if others can hear them say it. Why is this? I don't know, I suppose it's better than yellin obscenities.

On teh intranets, people do the same thing for some reason.