Even evil overlords put their pants on one leg at a time. Just because he has an evil empire to run, doesn’t mean his responsibility of personal hygeine and everyday duties comes to an end. In fact, for someone who interacts with so many acolytes, its important to smell fresh.
Darth Vader, much like any universe-domineering dictator, still manages to brush his teeth and shower everyday, and now, we have proof of that very fact.
