This is a new feature added to the Pro version. On a schedule you pick, from every 15 minutes to 4 hours, YouMeScript takes a backup of your collaborative script, and backs it up to a text-format file in a folder in your Drive. Once you set it up, this happens automatically in the background, and never slows down your main page, so you really don't need to think about it again.
"Why do I need backups, since the script is held in Drive?"
The best answer to that is "I don't know, and nor do you" which is exactly why you need them. Problems people have asked me to fix include deleted files they couldn't recover, and changes by collaborators. Automatic backups give you the ability to deal with those situations, and a bunch more.
A collaborative file is not like a regular file which you can just copy around all over the place for safety; by definition it's a singleton that multiple people can work on, which contains all the changes that everyone makes. You can't just copy it.
Recovering from a backup copy
If the worst has happened, simply pick "Import from backup", and choose the file you want (the backup date is included in the filename). There will likely be multiple versions of the script available from that day, and you can choose which one you want. YouMeScript creates a new fully collaborative normal script, which you can save to any name you want.
As ever, let me know any problems.