I read the info and understand what it’s supposed to do, but am curious about it. Does it, basically, take a snapshot of the system and keep it for reference in case of virus infection? Do any of the other antivirus programs have such a feature?
Can you click on ‘FAQ’ in my signature and browse for the entry VRDB?
Most you need to know about it you will find there 
I suggest you also read the help file and make yourself familiar with Avast, the settings it is offering the user and the terms that are used.
Just a little info from the help file about the VRDB:
VRDB stands for "Virus Recovery Database"; it was known as "Integrity Database" in previous avast! versions. The aim of VRDB is to help when, despite all the security measures, a virus gets inside the computer and the files are infected. With the help of VRDB, it is possible to repair infected files (return them exactly to their original state). VRBD is announced by an icon with the letter "i" in the system tray (next to the clock). If the icon is animated, the database is being created right now.