As a reader of many on line product reviews, I am always interested in the time this review is relevant for. As time pass things change and review get stale.
If you have this need as a webmaster and your review is file based (as appose to DB) you can use the filemtime function to automatically generate the last updated:
$LAST_UPDATED = date ("F d Y", filemtime('review.php'));
Where review.php is the file that holds the product review for example.