The ‘one frame’ goal is another form of reductionism. By definition, the simplest ad needs only one cut, or camera set-up (not including the end frame).
This is not a rule you need to place on every script you write, but it is a useful tool because it forces you to keep it simple.
Aim for as close to one frame (two or three is good, too), or at least be in a position to capture the basic idea in a single frame, as if it were a poster, even if the final ad uses more frames to improve the story telling.
Advertising Concept Book (Second Edition) by Pete Barry