Soccer's the most commonly associated sport with a draw no bet. It adapts the 12 market, which is a home win, away win, or draw, and changes it to a home or away win. As stated above, the stake will be refunded if a bet is placed on a home or away win, and the game results in a draw.
The biggest disadvantage of betting on this market is the low odds you get. If you back the home win in the standard 3-way match winner market, you will get much higher odds than if you do that in the 2-way Draw No Bet line. Also, while a draw returns your money, it doesn't give you anything other than that.