"Close lid to encrypt" aims to improve the privacy of your data. When you close the lid of your notebook, it goes into sleep/suspend mode. All processes are frozen and don't need to access your hard disk anymore. We use this opportunity to clean the keys of your encrypted devices and suspend them as well. Therefore, the data on your hard drive is protected. When resuming your computer, you must re-enter the password of your encrypted volumes. But then you're just where you've been working before.