First, they'd run the same headlines as 24 hours before. It's redundant, and can also be needlessly alarming: Hmm, was that "new" case of anthrax really "new" or the one from yesterday ?
Second, the kind of news that's being put on crawls is pretty silly. Do we really really need to know that Tom Hanks will receive some kind of achievement award while we are watching Donald Rumsfeld give a briefing ?
Third, the crawls create clutter. I am used to having a lot of windows on my computer screen, but normally they aren't competing with two stock tickers and other insets.
Fourth, the crawls create a false sense of urgency. What kind of visual emphasis is left if something really interesting happens ?
In conclusion: feh !