The larger vacuole in the plant helps the structure of the plant more. An example would be when you see a not watered plant and it looks droopy. It's because the vacuole has no water or waste in it to help with the structure. Plus, the vacuole is able to contain more in a plant cell. This is needed because animals can go get water or food when they need it, but plants are stationary and they have to use what they have stored.
