Every chunk you send at the mortgage kills future interest, which is the point of sending it. It also means less mortgage interest to deduct, and sooner or later somebody in your life will raise that as a reason not to do it.
Most people don't deduct mortgage interest at all anymore. The standard deduction roughly doubled starting in 2018, and the share of filers who itemize dropped hard. If your mortgage interest plus state and local taxes plus charitable giving doesn't clear the standard deduction, you're taking the standard deduction, and the mortgage interest is doing nothing for you on the return. Paying it down faster costs you zero in deductions, because you weren't deducting anything in the first place.
If you do itemize, the deduction is a percentage, not a refund. In the 22% bracket, a dollar of mortgage interest saves you 22 cents of tax. You paid a dollar to keep 22 cents, and the lender kept the other 78. Nobody takes that trade when it's put in front of them as a trade.
The deduction also shrinks on its own whether you chunk or not. A mortgage amortizes, which means the interest share of each payment falls every month while the principal share rises. The interest in year 20 of a 30-year loan is a fraction of the interest in year 2, and why your early mortgage payments barely touch the principal shows that curve. A chunking plan moves you down the curve faster. It doesn't create a loss you weren't already headed toward.
There's a real version of the concern and it's narrower than the version people repeat. It applies to a household that itemizes every year, carries a large balance at a high rate, and sits in a high bracket. For them the deduction genuinely reduces the cost of the mortgage. A 7% mortgage in the 32% bracket, fully deductible, costs something closer to 4.8% after tax. That's the number to compare against what your line of credit charges and what the money would earn somewhere else, and pay down the mortgage or invest the surplus runs that comparison. I answered the same question on camera in house first or investments first, and the after-tax number is what decides it there too.
Interest on a home equity line of credit follows a different rule and mostly doesn't help. It's deductible only when the borrowed money was used to buy, build, or substantially improve the home securing the loan. Money borrowed to pay down the mortgage itself doesn't qualify, and neither does money borrowed to park a paycheck. Is your HELOC interest deductible goes through the test.
I'm a licensed insurance broker and not a CPA. Brackets, the standard deduction, and the rules around all of this change, and your return is specific to you. Pull last year's 1040 and look at whether you itemized. If you took the standard deduction, the mortgage interest argument against chunking doesn't apply to your household and you can stop carrying it around. If you did itemize, take the numbers to your accountant and ask what your after-tax mortgage rate actually is. That one figure settles the argument.