Very helpful for making changes to a site and letting people know when the site will be back. Several themes to choose from. Lots of other options. Easy to configure. Just remember to set your IP as an allowed address before turning it on and remember that you are in maintenance mode before making a change to your URL or you'll have to delete it to get back to your admin page. Then reinstall it--your settings will be kept.
Especially helpful when you need to shut the site down to make fixes after being hacked.