It is recommended to treat Unit as any other type and to write it explicitly in method declarations.

* Reference: The talk "Scala with Style" by Martin Odersky at ScalaDays 2013

Hint: You can use Analyze / Run Inspection by Name (Ctrl+Alt+Shift+I) to apply this inspection to the whole project

Old description:
Unit result type annotation is redundant:
  // excessive clutter
def foo(): Unit // concise form
def foo()
* Refer to Programming in Scala, 2.3 Define some functions