For mining, If a GPU was failing in such a way that it was giving completely wrong output for functions during mining, that'd only be visible as a lower success

For mining, If a GPU was failing in such a way that it was giving completely wrong output for functions during mining, that'd only be visible as a lower success hash-rate which you might not even notice unless you did periodic testing of known-target hashes. For graphics, the same defect could be severe enough to completely render the GPU useless.