That way, one has the data available all the time on the original cards, even if any hard disks fail.
an 8 GB CF Ultra 200x card sells for Rs 2000. So, if one did not reuse cards, and shot to about 200 cards or 'exposed' 80 hours of video on a Canon 5D/7D, one would spend Rs 4 lakhs.
Rs 7.5 lakhs for 50 hrs of HD tape, or
Rs 4 lakhs for 80 hrs of Canon HD video.
I think its clear CF cards, as a medium, are way cheaper than HD tape or film. And if one does not erase and use the costlier film or HD tape, what reason is there to erase CF cards that cost 1/30th what film costs.