Owners of Macbooks who upgraded to an SSD might want to use this feature and here are two ways to achieve that:

• There is a tool called TRIM Enabler, that does this for you the easy way. Click here.
• For people who want to do it the manual way, here are the shell commands:
  

  sudo cp /System/Library/Extensions/IOAHCIFamily.kext/Contents/PlugIns/IOAHCIBlockStorage.kext/Contents/MacOS/IOAHCIBlockStorage /System/Library/Extensions/IOAHCIFamily.kext/Contents/PlugIns/IOAHCIBlockStorage.kext/Contents/MacOS/IOAHCIBlockStorage.original

  sudo perl -pi -e 's|(\x52\x6F\x74\x61\x74\x69\x6F\x6E\x61\x6C\x00{1,20})[^\x00]{9}(\x00{1,20}\x51)|$1\x00\x00\x00\x00\x00\x00\x00\x00\x00$2|sg' /System/Library/Extensions/IOAHCIFamily.kext/Contents/PlugIns/IOAHCIBlockStorage.kext/Contents/MacOS/IOAHCIBlockStorage

  sudo kextcache -system-prelinked-kernel

  sudo kextcache -system-caches

   These 4 command should do the trick as well.