You need to set a timeout period (3/6/9/12 months), add your phone number and contact details for up to 10 trusted friends or family members (email addresses and phone numbers), then decide if you want to share Google Takeout for services like Blogger, Picasa Web Albums, YouTube with those people and delete your account once it's inactive. Google will alert you one month before the timeout period expires.
It's a feature that seems to be useful if you want Google to automatically delete your account when you're no longer alive and share some data with the people you trust. Unfortunately, not all the Google Takeout data is easy to use. YouTube videos, Picasa photos, Drive files and Gmail's contact files are easy to open, but the data from Google+, Blogger, Reader is more difficult to read. When you set up this feature, you can pick the services you want.
You can also use the Inactive Account Manager just to notify friends and family members that you no longer use that account or to send an automated response to all incoming Gmail messages once your account becomes inactive.