That means you can use it to avoid any targeted spell, any board wipes that destroy things instead of exiling them or just use it to avoid losing creatures in a big attack
What's not to like
Sometimes there are things that you just cant let stay around
Just like Cursed Mirror and Midnight Clock, there are color-specific rocks at four mana that I cant neglect to mention
If you play something like Elves, Goblins, Humans, or Merfolk, you can fill your deck with 30 creatures of the right type and never worry about your mana curve because these creatures exist at all reasonable points in the curve, but if you ever play 30 Giants in a deck, then the average converted mana cost will be five and you will lose most games without ever casting a spell
It eventually becomes inevitable that your attacking creatures represent lethal damage with either their power, or dying and Kardur's life drain trigger, kind of like a Wicked role token