In case it wasn't clear from the above example: positional arguments
are for those pieces of information that your program absolutely,
positively requires to run.
A good user interface should have as few absolute requirements as
possible. If your program requires 17 distinct pieces of information in
order to run successfully, it doesn't much matter how you get that
information from the user--most people will give up and walk away
before they successfully run the program. This applies whether the user
interface is a command-line, a configuration file, a GUI, or whatever:
if you make that many demands on your users, most of them will just give
up.
In short, try to minimize the amount of information that users are
absolutely required to supply--use sensible defaults whenever
possible. Of course, you also want to make your programs reasonably
flexible. That's what options are for. Again, it doesn't matter if
they are entries in a config file, checkboxes in the ``Preferences''
dialog of a GUI, or command-line options--the more options you
implement, the more flexible your program is, and the more complicated
its implementation becomes. It's quite easy to overwhelm users (and
yourself!) with too much flexibility, so be careful there.
