Background app refresh is a great new addition to iOS 7. It allows apps like Todo to refresh their content in the background when the app is not actively being used.
According to Apple (http://support.apple.com/kb/ht4211):
"iOS learns patterns based on your use of the device and tries to predict when an app should be updated in the background. It also learns when the device is typically inactive, such as during the night, to reduce update frequency when the device not used."
Todo participates in the background app refresh as long as you do not disable it in your device settings. However, keep in mind the following when using iCloud: