Knowing the priority order in which things should be made is hugely important. Even the smallest changes to the story or base game mechanics can have rippling effects across the whole game, potentially leading to a lot of wasted development effort.
One way of quickly communicating and visualizing dependencies between tasks and parts of the game is to create a dependency stack, a diagram that lays down the various game features and pieces of content and the relationships between them (you can use the same tools as when creating a menu flow). Note that this is not a tool that helps communicate the structure or flow of the game; it's used purely to prioritize tasks.
If diagrams are too much, a simple spreadsheet can ...
