It--of course--depends entirely on your circumstances, the details of the loan, etc.
I have low rate, fixed 30-year mortgages, and plan on keeping them the entire time.
If there's ever an opportunity to refi at such low rates in the future (10, 20, or 30 years from now), I'll cash out refi and invest the money.
Inflation is the number one enemy of the early retirees, and fixed-rate mortgages are just about the best inflation hedge you can have.
The idea of paying them off makes me feel icky. Like it'd be selfish--sub-optimal, just to own them "free and clear" or whatever. And if I paid them off, far too much of my net worth would be in real estate. I'd much rather diversify.
YMMV. Paying them off, of course, is not a bad strategy at all. And it's essential for certain types of appreciation plays that are only cash flow neutral (and will have a very low rate of return, paid off, but one is anticipating high amounts of appreciation). It entirely depends on the details, just sharing my perspective on mine. :)