Back then, it was used to develop algorithms for real-time MPEG-2 encoder silicon. It can also be used to look at strategies used by other encoders (for example, ffmpeg). MPEG-2 video is still being used today, so it's still relevant.

Here's another screenshot showing the options available with the tool. You can switch between the picture (shown), macroblock type, macroblock quantization, number of bits per macroblock, motion vectors (shown in the previous screenshot) and coded block pattern.

http://www.w6rz.net/ss5.png