You see it a lot when you need a function that isn't exported by default. For example

use CGI qw/escape unescape/;
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allows you to use the escape and unescape functions as if you had defined them in your namespace.

use strict;
use CGI qw/escape unescape/;

my $escval = escape('test script');

print "Escaped: $escval\n";

my $val = unescape($escval);

print "Unescaped: $val\n";
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Outputs

Escaped: test%20script
Unescaped: test script
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