Maybe I am missing your point, but what do you mean, 'you cant take a reference of a hash element'? Why not? 
use strict;
my $x = {};
$x->{a}->{b}->{c}->{d} = 'watermelon';
print  $x->{a}->{b}->{c}->{d} , " is quite delicious\n";
my $ref = \   $x->{a}->{b}->{c}->{d};
$$ref = 'cantelope';
print  $x->{a}->{b}->{c}->{d} , " is quite delicious\n";

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And when you say, why would you want a reference to a hash or array element, when you can just say $x{key} or $y[$index]? I'd answer, one reason is that you may be dealing with something expects a reference to a scalar.

For example, think about implementing a toy spreadsheet in Tk. (Scary thought!) A reasonable data structure for a toy implementation would be an LOL of scalars, with references to each array element bound into a TK widget for display and updating. You'd need refs to every cell because (in this case) Tk wants refs.

In reply to Re^2: pointer memory and dynamic memory by water
in thread pointer memory and dynamic memory by pmtolk

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