Why is vacuum filtration sometimes preferable to ordinary gravity filtration?

Vacuum filtration is used instead of gravity filtration in order to achieve a dryer product in less time. The faster process of vacuum filtration allows the slurry to remain cold and in cases such as with benzoic acid more crytals will remain formed at colder temperatures. Gravity filtration is most useful when the solid is to be discarded and the filtrate (the liquid that flows through the filter paper) kept. Vacuum filtration is often faster than gravity filtration and is most useful if the solid must be kept or if a filtration must be done rapidly. A vacuum from an aspirator or a vacuum pump is used to pull the liquid through a funnel containing a piece of filter paper, while the solid is left on the paper.