Consider the following code:

  class C(val a: Int)
  new C(a = 10, b = 15) // too many arguments for constructor C: (a: Int)

Here, it's easy to see that argument b is superfluous. However, if constructor has considerably more arguments (e.g. 10+), finding excessive arguments becomes a non-trivial task. Error message should provide the list of excessive arguments, as not enough arguments compiler error does.