The Juicing Room is a room in the Wonka Chocolate Factory, specifically for juicing fruit.
The purpose of the Juicing Room can only be guessed at, but it's very likely used for juicing fruits to use the juices as flavoring for candies.
The Juicing Room came in handy when Violet Beauregarde chewed on Willy Wonka's incomplete Magic Chewing Gum, and the effects of the dessert (blueberry pie) turned Violet into a large, balloon of a blueberry. The juice kept growing inside her, apparently, and she was taken to the Juicing Room. The 1971 film put more emphasis on the effects of the gum: if Violet wasn't juiced, she might explode (In theory, She might have been a blueberry forever if she wasn't juiced.)
The Juicing Room is only seen in the games.