->route will create a new route object, which has a method ->to that sets some attributes in the object.
There is no hidden magic and they should not touch parent or child routes, but default values (and captures) will be forwarded to child routes when matching a path.

# /foo
my $x = $r->route('/foo')->to(controller => 'bar');

# /foo/*
$x->route('/:action')->to(action => 'test');
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This would be a nested route example where defaults and captures get forwarded. (controller => 'bar' in this case)