Thoughts on paying down your principle early

[Matt Tennie]

I Have a rental property that cash flows about 1700$ a month, is it smart to pay down the principle sooner (30 year fixed) with the extra cash, or save for buying more houses?  or is there a best of both worlds, where as long as I have enough for another down payment, using some extra cash to paydown the principle makes sense in the long run.  Just trying to figure out whether paying down principle early makes sense in cases where mortgage payments don't come out of your own pockets anyway and it is a buy and hold property