The additional curlies add "visual weight", one sees immediately that

print $a, $b;
# and
print { $a } $b;
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do different things.

I don't usually use the curlies, but that's more a result from laziness and thoughtlessness than anything else.

I kinda like the Perl 6 way of doing it:

print $a, $b;   # print both variables
$a.print: $b;   # treat $a as a file handle
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That's not a realistic example. If you were printing two variables, it would look like

print $name, ", ", age;
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or

print "$name, age";
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And neither looks similar to the following to me:

print $fh $age;
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As for your Perl6 eaxmple, you can do the same in Perl5.

$fh->print($s);  # Perl5
$fh.print: $s;   # Perl6
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That might be true for debugging output, put otherwise usage of print is pretty diverse.

Ack'ing through my private Perl code I've found pretty many occurrences of print $variable, EXPRESSION and print $variable EXPRESSION where EXPRESSION didn't start with a quote that looked like a separator.

Perl 6 - links to (nearly) everything that is Perl 6.

$a.print: $b;   # treat $a as a file handle

Good thing you added the comment. I would have taken $a.print to mean the value of $a is to be printed out -- probably to handle $b.

Well, it's new syntax, so it's no surprise you need to learn somthing about it.

It becomes clearer if you think more about: A method call (and $a.print: $b is a method call) can have one invocant, but many ordinary arguments. Which one is special, the invocant or the first, ordinary argument?

When you see

$a.print: $b, $c, $d, $d;
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Do you still think that $a is printed to file handle $b? Or to all of the arguments, all treated as file handles?

That would be a very bad huffman coding...

If you pass a file handle to print, the default assumption is that you want to print to the file handle. Adding curlies doesn't change anything.

The reasoning you posted only makes sense if one assumes the file handle is badly named. The fix for a bad variable name is not to add silly curlies to print, it's to change the variable's name.