Can Someone Please Explain The Practical Need For Non-Technological Countdowns To Me?

I don’t mean when two or more people are going to kick open a door or lift somebody over a ledge and they have to coordinate their effort, as in “One, two, three, GO,” which isn’t really a count-DOWN anyway. I mean when some bad guy is going to push a button on a bomb or gun or some other weapon, and there is a countdown before the thing goes off. WHY? What practical purpose does this serve? Turbo lag? Plot device? Brain death? The whole NASA countdown bullshit always pissed me off. Get the rocket ready and freaking LAUNCH it, already. To quote The Right Stuff, “LIGHT this candle!” What jackass came up with this countdown paradigm? Push the button, kill the people, then move on.

Yeah, I know: this stupidity provides dramatic tension so Our Protagonist can swoop in, at the last second, to save the day. Really? That’s the best you could do?