Say you want an associative array.

With a hash, a lookup would look like

my $val = $hash{$key};
[download]

With the OP's structure, a lookup would look like

my ($val) = map $_->{value}, grep $_->{key} eq $key, @$data;
[download]

That makes it a "pathological" structure to use as an associative array. However, it's an appropriate structure to store ordered key-value pairs.