Unless you live in, say, Antartica, leaving your laptop in the cold isn't going to do any harm to it. The only real danger of low temperature is if the metal contracted too much and started peeling off its circuit boards. That isn't happening until very low in the negatives though (In other words, you'd be fine pretty much in all practical cases). This is the reason why the mars rover need to have electric heating to survive the cold Martian nights.

However, if you intend to turn it on, that's another story. The real obvious difference is how long your battery will last. Most batteries operate poorly at low temp so it might die really quickly until you can warm it up.