Always book refundable reservations for hotels that will allow you to cancel your booking. A vacation isn't a vacation if you can't do what you want. Saving 10 percent isn't worth being locked in when plans change.
Comparable discounts are available through organizations such as AAA, Costco, and AARP. Such savings are often the same as or better than prepaid rates and can usually be cancelled the day before arrival. Check back before your trip and rebook if the price drops.