The digital version of vertical blanking interval data is called VANC:
http://en.wikipedia.org/wiki/Vanc
The analog vertical blanking space carries closed captions, and possibly test signals and network data (back when analog network signals were used).
VCR and DVD outputs can contain Copyguard (TM) anti-copying pulses in this area. The anti copying pulses vary in amplitude and cause the automatic video level control in VCRs to go up and down in the opposite variation when recording. They also drive vintage TV set owners crazy because they show up in the retrace as white lines that come and go in the picture. Perhaps no-one on this thread is old enough to remember when video tape rental stores carried two versions of each title, so if you complained of lines on your TV, they would pull out a non-Copyguarded copy to rent.