Despite the perceived inconvenience this issue may present, it is expected behavior for Mac OS X. The operating system prefers to finish any open printing jobs (whether in progress or waiting to connect to a printer) before going into Sleep mode. If you are experiencing delays when attempting to put your Mac to sleep, check the printer queue:
- Choose System Preferences from the Apple icon on the menu bar.
- Choose Print & Fax.
- In the Printers list on the left side of the window, check the status (colored dot with current status in gray) under each installed printer.
- If any of your printers (or fax machines) are "In use," click the "Open Print Queue" button and delete or hold any print jobs that are delayed or attempting to print on a printer that may not be available.
- If none of your printers are set to "In use," you should be ready to put your Mac to sleep.