They are, as far as I'm concerned, a cancer across multiple genres, intended to do nothing more than extract money from unsuspecting players. (mmorpg.com)
Plus, turtle shells will bounce off of scenery even if it's on a subsequent screen, threatening to kill unsuspecting players. (hardcoregaming101.net)
Sadly, many also use it to get quick amount of cash from unsuspecting players. (joystikrevolution.com)