Unrealistic results are an indicator that something might be wrong with the model design or model choice which deserves investigating. Why is that such a bad thing?

If you're modeling investment growth and your model is:

  future_value = investment_amt * (interest_rate ^ num_years)

or

  future_value = investment_amt * (1 + (interest_rate * num_years))

you might realize after running it a few times and seeing incorrect results that the model is flawed (first case) or inappropriate (second case) and fix it to:

  future_value = investment_amt * ((1 + interest_rate) ^ num_years)