I'm using Exception::Class to define my exceptions classes, but I just stumbled into a design question. Should create lots of exception subclasses like this?

MyExceptions::SomeThingy
MyExceptions::SomeThingy::SomeSpecificError
MyExceptions::SomeThingy::AnotherProblem
MyExceptions::SomeThingy::DontDoThat
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But if the subclasses SomeSpecificError, AnotherProblem, DontDoThat aren't different, then why have them? I was thinking of replacing those subclasses with fields under SomeThingy. Like this:

MyException::SomeThingy' => {
        isa         => 'MyException',
        description => 'Bad things happen here.',
        fields      => [ 'descriptor', 'value' ],
};
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And then I throw them:

MyException::SomeThingy->throw(
            'error'      => 'You did something I didnt like.',
            'descriptor' => 'DontDoThat',
            'value'   => $bad_variable,
);
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Hmmm. So I guess my question is, if all those subclasses do the same thing, am I getting anything out of creating them all? Other than the name of the exception itself tells me something about the error? If that is all I am gaining, then doesn't using fields make more sense? I'm new to OO, and new to using Perl as anything other than a glorified awk. Thanks.

UPDATE: This page covers what I was asking, too, in the paragraph titled "Write Sensible Throws Clauses".