The restore menu is a new addition to editor. Early in the design of the editor it was decided to use the scenery.cfg file to contain all the additional information about groups and color markers that the editor generates. This was because there was no evidence that this harmed the flight simulator and seemed to be the intention of the key=value scheme of the file, and because there was no evidence that removing disabled sceneries from the file is an effective optimisation. All was well, however, there are some popular for-profit tools and sceneries available that are removing keys that it doesn't understand. I have tried to contact the developers of these tools to talk to them about this problem but they have not responded. I have therefore decided to work around them.
There are number of functions provided on the restore menu, however it is worth noting what the backup file is, and when it is created and updated. The backup is simply a copy of your last saved scenery.cfg, however it will only be updated if you have saved and, either closed the editor, or opened or reloaded the scenery file. This should prevent accidentally losing the backup information when you are editing, but you should be aware that once you have reloaded or closed the editor you will lose that old information.
The restore functions available are:
Restore Groups from Backup recovers the groups information from the backup file, which was the initial requirement for this functionality. There are a number of options: Restore groups only for areas that don't have groups listed, Restore the missing groups from the backup or simply overwrite the groups data with that in the backup. You can also restrict the functionality to work on the selected areas only.
Restore Deleted Areas from Backup will restore areas that are present in the backup but not in the main file.
Overwrite Scenery from Backup will simply copy the backup back over the main file.