Planning involves your making decisions, organizing, and coordinating the various elements that contribute to the production.
For simple productions, it is possible with experience and a modicum of luck to ‘work things out as you go’, and create from scratch on the day. While scenery is being erected and lit, you walk the camera and sound crew round the setting, explaining the action and probable shots, and then rehearse.
But don’t rely on this approach. At best it is makeshift. If you suddenly decide that you need three matching chairs instead of two, or a low glass-topped table, they may not be available unless you happen to have a sizeable property store to draw on.
Even where you cannot ...