Hummingbird storing huge amounts of data

I noticed that the amount of data used on my main site had gone up by over 200 MB to a total of 500+ MB in the past few days. This shocked me. I checked everything I could think of and could find no reason. Deactivating Hummingbird caused 300 MB to instantly drop away. This means that data was being cached and stored, I guess. I am guessing this is not the intended behavior... or is it? If data keeps increasing by that amount, I worry that I will soon be out of storage as more sites get added to the network.