Although we don't believe in timing the market or panicking over market movements, we do like to keep an eye on big changes -- just in case they're material to our investing thesis.

What: Shares of entertainment conglomerate Cablevision (NYSE: CVC) spiked more than 10% this morning, on news the company may spin off the AMC, Sundance, IFC, and Wedding Central channels, among other assets, as Rainbow Media.

So what: A whole isn't always worth more than the sum of its parts. Sometimes, it's just a hole into which value crawls to die. Cablevision is trying to unlock the value of its assets here, gambling that investors will pay more to own Rainbow and rump-Cablevision separately.

Now what: Cablevision calls this a "leveraged" spinoff -- suggesting that investors could find debt at the end of this Rainbow. Cablevision may burden its spinoff with a sizable chunk of the company's $11.7 billion in debt, freeing itself in the process. That would be good news for holders of the core company, but it may not be worth a 10% bump in price all on its own. Remember, spinoff plans don't always materialize. Unlike press releases, spinoffs take time to put together. Use that time to crunch the numbers and decide whether this spinoff would be good or bad news.

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Fool contributor Rich Smith does not have any position in any company named above. Fools may not all hold the same opinions, but we all believe that considering a diverse range of insights makes us better investors. The Motley Fool has a disclosure policy.