To save effort, you can mix building blocks of various abstraction levels (or sizes) in single scenarios, instead of showing all low-level interactions.

See the following example (building block hierarchy on the left, one scenario on the right)

Mixing abstraction levels saves effort

As you show some large or more abstract building blocks, you hide their internal working or internal processes within the scenario. In the example above, you completely hide the internal working of building block B… you simply don’t describe or specify what and how B is performing its tasks.