There is a big need to be able to expand and collapse the checklists. With the ability to add multiple lists, it can quickly turn into a long scroll to get through them all. With a long list, it becomes very hard to get a clear overview of the tasks that are within the given task.
The feature to expand/collapse is just the beginning to create a better and clearer overview of tasks within a task - it could need more, like assign an item to a team member and a form of labelling for prioritising instead of relying on which item is on top of the list.
Also, if all tasks are checked off, it would be nice if the list collapses on it's own or you can set it as a rule to automate it.