If his quickly means faster, let's compare those two solutions:

use Benchmark qw(timethese);
use strict;
use warnings;

my @array = (1 .. 100000);
timethese(100, {granfather => \&grandfather, usual => \&usual});

sub grandfather {
    return 1 if grep {$_ == 100000} @array;
}

sub usual {
    for my $a (@array) {
        return 1 if ($a == 100000);
    }
    return 0;
}
[download]

If the element we serach is at the end, grandfather's is a little bit faster:

Benchmark: timing 100 iterations of granfather, usual...
granfather:  4 wallclock secs ( 3.58 usr +  0.00 sys =  3.58 CPU) @ 27
+.95/s (n=1
00)
     usual:  4 wallclock secs ( 4.13 usr +  0.00 sys =  4.13 CPU) @ 24
+.24/s (n=1
00)
[download]

But if you change the above code to search for 3 (at the beginning of the array), then the usual way is much faster:

Benchmark: timing 100 iterations of granfather, usual...
granfather:  3 wallclock secs ( 3.58 usr +  0.00 sys =  3.58 CPU) @ 27
+.95/s (n=1
00)
     usual:  0 wallclock secs ( 0.00 usr +  0.00 sys =  0.00 CPU)
            (warning: too few iterations for a reliable count)
[download]

With something in the middle say 50000, the usual way is still close to 50% faster.

Benchmark: timing 100 iterations of granfather, usual...
granfather:  4 wallclock secs ( 3.69 usr +  0.03 sys =  3.72 CPU) @ 26
+.89/s (n=1
00)
     usual:  2 wallclock secs ( 2.08 usr +  0.00 sys =  2.08 CPU) @ 48
+.12/s (n=1
00)
[download]

Now you know which direction it is pointing to ;-)