Telecine/transfer houses often burn timecode, footage, and other useful information into the video while doing the transfer.  While useful, this video is quite distracting to look at while watching a cut.  Using a matte on a higher video track is unwieldy, and anyway you generally want the data to be visible in the Composer window, but not when going out to the client monitor.  Accordingly, I have seen numerous cutting rooms with ugly black posterboard taped to the client monitor(s) to mask off this extraneous information.

An elegant solution would be an option in the Video Output Tool that allows you to mask off the top and bottom portions of video going out of the system (but not the video displayed in the Composer window).  It would be quite handy if you could select how many lines are masked off each edge, much like the crop function in the PIP effect.

yale:

It would be quite handy if you could select how many lines are masked off each edge, much like the crop function in the PIP effect

Indeed, seconded, I've suggested such a feature a decade ago.

Thirded.

Didn't even know I wanted this until I read this thread. But having just masked off the editor's beautiful plasma with gaffers tape I think this would be a great feature

You can add my vote as well.