b frame strategy in ffmpeg

Can anyone explain to me, what b_frame_strategy actually does in ffmpeg's mpeg-2 encoder? I tried to understand this in the source code, but don't get the context in that ocean of C code. Please enlighten Thanks

This is from the Mencoder Manual.... I believe it is very close to the same as FFMpeg Code:

Thanks Fishman, That's helpful information for me to look deeper into those tuning options. Cheers