Comparing Adding More into Savings or Paying Extra Mortgage Principal Payment

Don't forget that in an inflationary environment which we may well be entering it is good to have debt because it gets inflated away. Most people pre-pay mortgages for emotional reasons or because they have poor impulse control and would just spend the money elsewhere.

More logical minds realize debt is good in an inflationary environment.

Debt is only good in an inflationary environment because the intrinsic value of your dollars is worth less than before.  However if you have one of those adjustable rate loans or mortgages, having a high unpaid balance will hit your pocketbook since you have to pay out more dollars each month.  The best scenario is not have any debt regardless of the interest rate trends.