Broken thingymajig

On my Bianchi Nirone like most bikes, there is a plastic circular disc. This is or rather was located on the rear cassette between the cogs and the spokes. One of the plastic lugs on it broke and the whole thing started to rub against the spokes so I took it off. Is it really vital and should I get it replaced :?
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However................you just might be the only one who would.
Me? I've got plenty extra weight, I don't need any more. Not even, almost weightless, plastic discs.
Damn........I hope I haven't spoiled my chances in the Giro D Italia 2011....