What makes a .screenflow file so large? Is it possible to compress the data?

I'm using Screenflow to record some FaceTime interviews. It's eating up my hard drive! A 30-minute very low quality video is 6 GB!! The screen (MacBook Pro 15" Early 2011), the microphone voice, and the computer voice are recorded. What is taking up so much space? Is it possible to reduce the size a bit? If so, how?