Imagine how strange would it be to drive a car that can move only straight forward, without steering wheel to turn it either left or right. Strange would also be to have a phone that can connect only to one phone. And what about a TV you can't change channel on ?
We're lucky to only read about these funny cases where the lack of choice could lead to a not very happy end. While computer software likes happy ends, it contains variety of functions, and some of them deal with flow control. Giving ability of choice, programmers make software interactive. Meaning, user is not watching a movie, but participating in interactive sessions between software and it's user.
The car will take you almost wherever you want, thanks to the steering wheel. To make MMB application go at desired path, you'll use steering wheel too - flow control functions !
MMB uses two ways of controlling script flow: If statements and For..Next loops.