The VRDB database is referred to by avast in order to attempt a repair of an infected file. If the file is one that is scanned by the VRDB process and has been scanned then a repair can be attempted.

Without the VRDB a repair can’t be attempted, leaving only the Move to chest or Delete the infected file (not so good when the infected file could be a system file).

So, the VRDB process is in my opinion essential to the avast anti-virus program.