Quoting completely from Remiel…
Ever since the PowerBook G4, Apple notebooks use a system called Safe Sleep to restore your computer to working order after being left unattended for a while. With Safe Sleep, the current session is written to both RAM and your hard disk — RAM because waking up is faster that way, and the hard disk so that the system can safely go into hibernation if the battery drains while it’s asleep.
Your computer will go into standby faster if you turn this off. You can also save some space on your hard drive by disabling Safe Sleep, and removing the sleep image. You’ll still be able to sleep your computer, but there’s no zero-battery safety net anymore. Your MacBook can go a very long time in RAM-only sleep mode on a full battery, so this should rarely affect your life. But keep in mind that if the battery does run out, you’ll lose any unsaved work.
This Macworld article goes into greater detail about Safe Sleep, but for our purposes, the short version is this:
- Open up Terminal.
- Type “sudo pmset -a hibernatemode 0” without the quotes, and hit Enter.
- Enter your password when prompted.
- You are now using RAM-only / “old school” sleep mode.
- Now type “cd /var/vm” and hit Enter.
- Finally: “sudo rm sleepimage”
- This will delete the existing sleep image file on your hard drive, reclaiming that space for future use.