When was the last time you were asked to take a dare? Not unlike those days when schoolyard pranks took a wrong turn, this kind of dare is more a wagered plus. You can still stake up to 3 coins in the base game and still make great wins just from pure luck. It still won't get you any closer to the Diamond Dare Bonus Bucks slot bonus round if you don't place a 4th coin. This unique feature won't increase the base game wins at all.
What it does do, can increase Bonus Bucks from the bonus game. As far as you can see, the pay table tells you all the info about wins in the game. Land a Bonus Bucks symbol on the 3rd reel from any spin, and this begins the bonus round. When will it happen is totally at random, thus this is why it's your dare to get there. Good luck!