Question: "Should I ever buy hotel or airline miles?"

Answer: Maybe. If a hotel chain or airline rewards customers by offering a promotion (for example, a 50% bonus on points), then it might make sense to buy them, but only if these two conditions are met:

1. You have an immediate use for them, meaning you can book something right then with them that you plan to do anyway, AND there is availability (you've already checked)

2. The value of that booking with points is better than the CASH price of that booking (obviously, I hope).

A couple of examples where this is a great scenario: 

• Booking Business Class Seats - If you find a great points deal for a flight, it's a great idea to check and see what it would cost to purchase those points, especially if there's one of the Bonus Points Promotions. Then compare what those points would cost you vs. the cash price of the flight. For example, a $4,500 business-class flight requires 75,000 miles, which could be purchased for $1,200, saving you money, and is a pretty sweet deal for business class. 
• For a hotel scenario, Marriott Bonvoy offers the 5th night free when booking a stay with points. When they occasionally offer their bonus points promotion, using it to earn 50% more points and then redeeming them to get the 5th night free can save you money compared to paying cash. 

So always keep this trick in your back pocket, check around if you see a bonus points deal like this, check the points vs. cash price and availabilty and you might just score you are great travel deal. You can use this Points Calculator to determine if it's a good deal or not!