It's interesting that most fictional depictions of legged robots (outside of explicitly humanoid robots) use digitigrade legs. Did the artists model their art after animals which happened to have these legs, or did they subconsciously realize that this would be more effective?
Isn't it obvious? After you see an ostrich running, there is little doubt about its efficiency.
Now, actually capturing that efficiency in a real system takes some really hard engineering work. Fictional robots do not need to conserve energy, compensate for impacts, etc.
