Throwing items is one of the basic ways to attack a monster (along with using a weapon such as a whip, or jumping on monsters).
Some items break after striking a monster:
Other items can be used to kill an unlimited number of monsters:
Throwing techniques
Pitching Gloves give the ability to throw items much further.
Normal bombs are usually most useful when dropped, but Sticky Bombs are very useful when thrown.
Be careful when you throw a Rock or Arrow at an enemy near a wall, you may be the victim of your own projectile. Both the Rock and the Arrow will deal 2 Hearts of damage to you!