Did you mean to write bias can have a positive impact, too? Any model or human will suffer from some degree of uncertainty. You can never say anything with 100

Did you mean to write bias can have a positive impact, too? Any model or human will suffer from some degree of uncertainty. You can never say anything with 100% certainty. If you know a patient had cancer before, the chance that they have cancer again is much higher usually than the general population. This is very valuable for diagnosis. It's good to have a prior/bias to check more closely here and err on the side of caution. It's good to check for the more likely explanations first when you have multiple competing hypotheses and limited capacity for testing.