Welcome to the forum.
You might want to look at this Wiki article: Paying down loans versus investing
The key point is that the extra mortgage payment is using some money, and the money could be used for something else. Instead of making an extra mortgage payment, you might contribute the money to your IRA or 401(k). This is a purely financial decision: which is the better use of your money?
For example, if your employer matches your 401(k) contributions, that is surely a better use of your money, as $1000 contributed to the 401(k) becomes $2000 immediately and then grows tax-deferred.
Similarly, if you are going to buy a new car in a few years, you could save the money (probably in a CD or money-market fund) so that you can pay cash for the car. Instead of saving on mortgage interest, you would save on car loan interest, and that is better because car loans are not tax-deductible while mortgage interest often is.
On the other hand, if your mortgage is at a high rate and you can't refinance it, then paying down the mortgage is a good use of your money; you save high-rate interest, and you are also paying down the principal toward the point at which you can refinance for a lower rate or get rid of mortgage insurance.
So, if you would like better advice, post the terms of your mortgage, and the alternative uses for your money. We suggest you use the format in Asking Portfolio Questions