Why do we need separate “.swift” files for each class?

Question

Wondering if you might be able to answer a very basic beginner question for me. I’m working through the Cocoa + Swift tutorial on Lynda and I’m a little confused about class

Answer 1

As good practice:

If the classes are unrelated, lengthy or used independently from other unrelated classes then they should be in separate files.

However, if the classes are tightly coupled with one another and are not lengthy then they could be in the same file.

This post also touches on this subject.