Thanx to Google-Books here the complete passage (underlining added)

Requiring the named arguments to be specified inside a hash ensures that any mismatch, such as:

$line = padded({text=>$line, cols=>20..21, centered=>l, filler=>$SPACE});

will be reported (usually at compile time) in the caller's context:

Odd number of elements in anonymous hash at demo.pl line 42

Passing those arguments as raw pairs:

$line = padded(text=>$line, cols=>20..21, centered=>l, filler=>$SPACE);

would cause the exception to be thrown at run time, and from the line inside the subroutine where the odd number of arguments were unpacked and assigned to a hash:

Odd number of elements in hash assignment at Text/Manip.pm line 1876

The only difference in error handling that I can think of might result from unquoted keys ... (?)