Mac notebooks: Wait for your computer to fully shut down before closing the display
If you decide to shut down your Mac notebook rather than putting it to sleep, be sure you allow it to shut down completely before you close the display.
You can tell when a Mac notebook is completely shut down by confirming you have a black screen, no active power light, and no fan or drive noise. If you close the display on a MacBook Pro, MacBook, MacBook Air, PowerBook, or iBook while it is shutting down, the computer may not shut down properly.
As an alternative to shutting down your notebook, consider simply closing the display, which puts the system to sleep.