[MEncoder-users] How important are B-frames?

[Sylvester 4]

How important are B-frames and does a video really need them?

"MEncoder's libavformat muxing is presently broken and can generate
INCORRECT files in the presence of B-frames. Moreover, due to bugs MPlayer
will play these INCORRECT files as if nothing were wrong!"

If I encode using -of lavf, the above is displayed.  So, I would set
bframes=0 thinking this must be the correct procedure.  But I am now
wondering if a video is suffering in quality due to zero B-frames in
the video.

Also, in MPEG-2 files, I notice they have - 99% of the time - BVOP.  I
think I remember it stands for bidirectional video object plane.  Is
this just another name for B-frames?