The continue block is guaranteed to be executed in each iteration.

my $i = my $j = 0;
while ($i++ < 5) {
    next if $i == 2 || $i == 4;
    print "i:$i\n";
}
continue {
    $j++;
    printf "j:$j\n";
}
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See that the i line is not always printed because it depends on if checking, while j line is always printed regardless what happens inside the while block^*. This won't happen if printing j line is put inside the block as i.

But frankly, I never use continue myself in practical. It exists for some reason regarding the for loop (see Programming Perl). From the doc:

"last", "next", or "redo" may appear within a "continue" block. "last" and "redo" will behave as if they had been executed within the main block. So will "next", but since it will execute a "continue" block, it may be more entertaining.

Some monk commented on that emphasized text but I can't recall the node.

* Unless redo take place, as shown by GrandFather below. The same thing with last. Consider,

my $yodda = 0;
while ($yodda < 6) {
    last if $yodda == 5;
    redo if ++$yodda & 1;

    print "Even is ";
} continue {
    print "$yodda\n";
}
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Update: added note following correction by GrandFather