Often, the point of masks in Legend of Zelda is to give Link an ability he didn't naturally have on his own, or to enhance a natural power. For the Bunny Hood, it gives Link a much needed boost in speed.
Not so ironically, in both Ocarina of Time and Majora's Mask, the Bunny Hood gives Link incredibly running speed. Which can be great when you're fighting monsters, or trying to flee, or trying to solve a puzzle in the correct amount of time.
In fact, in Majora's Mask, the key to getting a few of the masks in the game required that you use the speed boost you get from the Bunny Hood.