What the Camel does or doesn't say is mostly irrelevant. If your coding standards allow for exit() within a subroutine, then use it. However, most of the community has come to expect die() within subroutines and exit() (if it's even used) from the main scope.

Now, die() and exit() do different things. The biggest difference is

eval {
    print "Inside\n";
    die;
};
print "Outside\n";
----
Inside
Outside
[download]

vs.

eval {
    print "Inside\n";
    exit;
};
print "Outside\n";
----
Inside
[download]

exit() exits, end of story. die() allows for some manner of error trapping. This is the main reason why die() is preferred within subroutines. You may want to reuse that subroutine somewhere else that wants to be able to trap the abnormal termination. Also, die() triggers $SIG{DIE}, which can also be useful to trap.