The World of Warcraft: Wrath of the Lich King expansion features quicksilver rewards. These are special in that they allow the player to receive a special type of XP in the game. This type of XP is called Silvervenging, and it allows the player to double their XP through the use of quicksand. There are several quests and activities in the game that allow the use of quicksilver rewards, but they are not mandatory.
If you are leveling up, you can use a quicksand recharge on a variety of things across your adventure zone. These include all of the quests in the zones in which you progress through the game; those that take you out of town; and even some boss quests. The quicksand used is not part of the item that you get when you complete the quest, it is added to your inventory instead. Using a quicksand recharge will restore you to full health and allow you to fight more easily against tough enemies.
Silvervenging is only useful for a limited amount of time though. After reaching a certain level, the effects of using quicksand on items wear off and no longer grant experience. This makes it not very effective as a leveling path, even if you are just getting started. It also makes it difficult to make gold by using quicksand to make gold chests and such, since you can never have enough of them.
There is an exception to this. Quicksand does give the user an increased speed when moving. This is especially useful for running away from battles or battling bosses. However, this is a fairly small advantage. For the most part, the only reason to bother with it is to gather gold. You can always use the extra gold for whatever purpose you have in mind.
There are some items that can only be obtained through the use of quicksand. For example, the item soulbound allows the player to pick up one soul per game session. Soulbound is a form of currency which players earn throughout the game. Once the player uses it, they get a certain amount of experience in return. Soulbound is worth its weight in gold, but it isn't nearly worth it in experience.
So do keep your eyes open for items that can only be gotten through quicksand. The faster you use it, the more gold you will make. Of course, . . . . . . there are other ways to gain gold besides using it. Gambling, farming, and auctioning the work just as well. Find out what other alternatives you have to gain gold rather than using quicksand.