Earlier quoted context omitted.
The mortgage deduction on it’s own isn’t such a big deal but it suddenly makes a lot of things tax deductible which aren’t if you take the standard deduction. The tax code is complex largely to enable such seemingly subtle interactions.
What kind of stuff becomes tax deductible once you get beyond the standard deduction, that doesn't involve having a business, which doesn't have that standard deduction limit anyway? Charitable donations? Medical expenses if you have a really bad time and need to spend more than %4 of your income to cover it?
However, some oddities like theft of investments such as gold or artwork and even some fines can be deductible. So sure on it’s own the mortgage tax deduction isn’t always huge, but it’s rarely the only deduction someone could take.