Martin Odersky

“Inheriting from Application is shorter than writing an explicit main method, but it also has some shortcomings. First, you can't use this trait if you need to access command-line arguments, because the args array isn't available. For example, because the Summer application uses command-line arguments, it must be written with an explicit main method, as shown in Listing 4.3. Second, because of some restrictions in the JVM threading model, you need an explicit main method if your program is multi-threaded. Finally, some implementations of the JVM do not optimize the initialization code of an object which is executed by the Application trait. So you should inherit from Application only when your program is relatively simple and single-threaded.”
― Martin Odersky, Programming in Scala

“You may be wondering why you can't access the elements of a tuple like the elements of a list, for example, with "pair(0)". The reason is that a list's apply method always returns the same type, but each element of a tuple may be a different type: _1 can have one result type, _2 another, and so on.”
― Martin Odersky, Programming in Scala