Argument Picker is a simple API to access and elaborate arguments in a flexible way.
Basically it allows, given URL arguments like:
to retrieve one of those arguments through a function:
which - in the specific example - would return "Volkswagen".
This module essentially adds the possibility to assign labels to arguments, through this syntax:
and then allows you to retrieve any argument using the label as a reference.
Some of the helper functions are dedicated to specific modules (i.e. Views), enhancing the accessibility of arguments:
Assuming "your_view" has a "foo" argument, using argument_picker, you could easily setup this argument's default value with:
<?php return arg_picker_get_view_argument("foo"); ?>
which would return "4" (for the example above) or "all" (when the argument is not present).
Basically it's just an alternative to an url querystring with Drupal-specific add-on features, which comes extremely useful when implementing progressive filters (like a faceted search) through views but it also comes very handy for retrieving arguments in dynamic PHP blocks, panel panes, custom modules or wherever you want.
Not to mention that a normal querystring is still usable:
leaving every other querystring-related features intact.