It's been ages so I'm fuzzy on the exact details but there was a common problem encountered with mod_perl (where people initially would frequently use the CGI compatibility wrapper) where people would have named subs nested and then got warnings about "variable $foo won't stay shared at ####" because the inner sub would get bound to one my variable while the outer would have a new one reallocated on its pad. Again, fuzzy but something like this (not that this is at all useful code) <handwave>

#!/usr/bin/env perl
use 5.034;

sub outer {
  my $foo = $_[0];
  sub inner {
    say "foo: $foo";
  }
  inner();
}
outer( "bar" );
outer( "quux" );

sub outer2 {
  my $foo = $_[0];
  my $inner = sub {
    say "inner2: $foo";
  };
  $inner->();
}
outer2( "bar" );
outer2( "quux" );
__END__
foo: bar
foo: bar
inner2: bar
inner2: quux
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Having the inner sub be an anonymous sub makes it a proper closure.

Edit: And the reason this was a frequent problem under mod_perl was that the CGI compatibility wrapper (Apache::Registry I think?) would wrap up the entire CGI script into an anonymous sub that it would run during the content phase so any named subs in the script were then nested subs.