It seems obvious that test pass rates are important.  The higher the pass rate, the better quality the product.  The lower the pass rate, the more known issues there are and the worse the quality of the product.  It then follows that teams should drive their pass rates to be high.  I’ve shipped many products where the exit criteria included some specified pass rate—usually 95% passing or higher.  For most of my career I agreed with that logic.  I was wrong.  I have come to understand that pass rates are irrelevant.  Pass rates don’t tell you the true state of the product.  It is important which bugs remain in the product, but pass rates don’t actually show this.

Good description of the trick to delete bugs in Bugzilla.