When a scenario has too many steps, it becomes hard to read & follow. Using nested step helps to clean up the scenario, & helps promote reusability of groups of steps, think of it as code refactoring.
Very often, we tend to repeat a number of common steps in all scenarios within a feature, to dry things up, as well as improve readability (helping reader to better focus the intent of each scenario), we can use 'Background'.
Data setup is sometimes painful in features writing for cucumber. Use pickle & factory of ur choice to make it less painful.