A. There is no one clear-cut answer as it depends on every family's unique situation.
Here are some of the important factors to consider before arriving at your final decision:
Mortgage interest rate: the lower the interest rate (remember the interest is deductible too), the less incentive you have to payoff it earlier, especially if your investment return is higher than mortgage interest rate.
Source of funds in retirement: if most of your retirement funds is in 401k, you will incur a hefty tax by withdrawing funds from 401k. It's unwise to payoff mortgage by withdrawing money from qualified retirement plans. If you have ample liquid cash outside of retirement accounts, then it's okay to consider paying off mortgage early.
Guaranteed income in retirement: if you don't have a large amount of guaranteed income in retirement, such as pension, social security, and annuity, that is more than enough to cover mortgage payment and other expenses, then it's a good idea not to pay off mortgage.