Well, you could but I don't know why you'd want to.

In the following script (using Benchmark) you'll see:

• splice is relatively less efficient. I also suspect it might have future maintainers scratching their heads wondering why it was used ("splice @array, 0, 1" has identical functionality to "shift @array" — it's just slower and requires more keystrokes to code).
• shift is more efficient than splice.
• My original map is faster than both of those; it doesn't destroy the original array; and it's a lot less coding.

#!/usr/bin/env perl

use strict;
use warnings;

use Benchmark qw{cmpthese};

cmpthese -1 => {
    splice_unique => \&splice_unique,
    shift_unique  => \&shift_unique,
    map_unique    => \&map_unique,
};

sub splice_unique {
    my @sorted = sort qw{q w e r t y q w e r t y};
    my $last = '';
    my @unique;

    while (@sorted) {
        my $element = splice @sorted, 0, 1;

        if ($last ne $element) {
            $last = $element;
            push @unique, $element
        }
    }
}

sub shift_unique {
    my @sorted = sort qw{q w e r t y q w e r t y};
    my $last = '';
    my @unique;

    while (@sorted) {
        my $element = shift @sorted;

        if ($last ne $element) {
            $last = $element;
            push @unique, $element
        }
    }
}

sub map_unique {
    my @sorted = sort qw{q w e r t y q w e r t y};
    my $last = '';
    my @unique = map { $last eq $_ ? () : ($last = $_) } @sorted;
}
[download]

Representative result:

                  Rate splice_unique  shift_unique    map_unique
splice_unique  93699/s            --           -5%          -20%
shift_unique   98642/s            5%            --          -16%
map_unique    117028/s           25%           19%            --
[download]

Ah ok, I thought slice would not involve pushing the unique elements into a new array, rather remove them "as-you-go" if the array is sorted, since they would be next to each other...