Dependency management is a critical and often overlooked area.
Waterfall lived and breathed on dependency management, encapsulated in the many dependency types one could capture in Gantt charts (Finish/Finish, Finish/Start etc.). However, the complexity in maintaining this often pushes it to becoming ‘tomorrows’ action, again.
Other methodologies such as Agile, can give the illusion that this is no longer the challenge it was in Waterfall. But it still is, albeit in smaller, incremental steps that allows for course corrections more often, i.e., as a key dependency arises, it is often managed in real time. Whereas in Waterfall one is trying to predict such dependencies months and even years ahead.