Very often you may want to breakdown a project into big User Story and from there you create small tasks. Depending on how your company/team works, you may have many-level hierarchy of tasks. Looking at the hierarchy is quite helpful because you know which tasks belong to which parts.
However, hierarchical view does not go together with Kanban board. For example, Trello does not support card hierarchy.
Some company uses real, physical Kanban board. That case will be similar to trello - cards are cards and cannot be represented physically as "children" of other tasks.
Without hierarchical view, you will not be able to see "big picture" of project. How do you overcome it?
Disclaimer: I am currently managing projects using Redmine which supports both hierarchical view and Kanban-view (although Kanban-view is rather too simple and works not as smooth as Trello)