Rafael commented some time ago on a quick way to put Macs to rest, long before the launch of the new MacBooks unibody. However, after a few days using the notebook presented at the end of last year, I noticed something different in his behavior whenever the battery runs out.
Before, when a MacBook or MacBook Pro used up its battery, the system went into Sleep mode, with the white light indicating that the computer was still active, requiring only the connection of the outside cable to quickly get back to work. The computer stayed that way until the battery was completely drained, leading to the mode known as Safe Sleep, described in the last paragraph of this Apple support article.
Safe Sleep mode is characterized by the storage of RAM data on the computer's hard disk. This is necessary so that there is no loss of information if the energy that keeps the memory running runs out. For example, if someone unplugs the power cord from an iMac in Sleep, all running data will be lost.
In the new MacBooks, however, Safe Sleep mode seems to come as a standard: when the notebook's battery runs out, it then shuts down, without white light "breathing" or anything. When reconnecting the power cord, it is necessary to press the On / Off button to return the system to the last state before actually hibernating.
On the one hand, such a system guarantees data integrity, but on the other it ends up being a bit boring boot on the computer even with the battery having a minimum charge. In Rafa's tip, you can see the procedure for making the necessary changes to these adjustments, via Terminal.
Another alternative would be to use the free program SmartSleep, with a graphical interface and easier to understand your Mac's rest options, or in the case of the new MacBooks, return to the ?Sleep + Safe Sleep? configuration.