use strict;
use warnings;
use 5.010;

sub do_stuff1 {
    given($_[0]) {
        chomp;
        say;
    }
}
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What, if anything, is gained by inserting a control statement (given) here in a context where it shouldn't ever affect the program flow? Are you just showing another way to do it or is there some subtlety to given which I have failed to grok?

It's "just" another way to do it.

What's the point of writing anything you write one way, and not another way?

given is a syntactically nice way to to assign to my $_, which I happen to like. I don't see why it has to be connected to control flow. (Which is also the reason why the given/when construct is not spelled select/case in Perl: both given and when can be used independently).

The strength of the topic variable $_ is that you can use it without writing $_ explicitly. given takes this one step further and makes the assignment also implicit.

I also happen to like given because in Perl 6 you can call any method doit on $_ by writing .doit, the method doesn't have to be special for that in any way.

So when you write lots of method calls on the same object, you can save a typing this way:

# Perl 6 code here
given $svg-canvas {
   .rect: x => 5, y => 5, height => 90, width => 190;
   .circle: cx => 100, cy  => 50, r => 20, style => 'fill: black';
   .text: 'Some caption', x => 20, y => 15;
   # etc. 
}
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Perl 6 - links to (nearly) everything that is Perl 6.