It usually gets spent in some “need” that pops up.

When it’s not available it doesn’t get spent.

I paid off my 3.75% RJ fo home, and was able to bring over 200k to closing on a “mainline fo” home.

Hard to itemize deductions as an RJ pilot so the mortgage interest deduction is a wash.

The loss of investing the money is real, but it is the price of risking poor discipline/ material fights of cash just sitting around looking for a reason to be spent.

Whenever/if interest rates drop back to <4% a cash out refi is only a phone call away.