A few cracks can make a world of difference:
GE Hitachi Nuclear Energy said it had discovered extensive cracking and "material distortion," and likely would recommend that the boiling water reactors using its Marathon control rod blades replace them more frequently than they had been told to previously.
"The design life if not revised, could result in significant control blade cracking and could, if not corrected, create a substantial safety hazard and is considered a reportable condition," the company said in its report to the NRC.
And yes, they're kind of important. That "material distortion" can inhibit full insertion, which is, you know, not good. But when I saw this: