What a good idea

On the +positive+ side, have seen WDO used to get rid of FBI ransomware that has blocked a computer.

Since WDO scans a computer before the Operating System loads, it can go around the lockdown and remove the infection.

Have not tried it yet, however, may give it a whirl when the opportunity appears.
Brink has a good tutorial: Windows Defender Offline

Looks as if it would be best to use a USB flash/pen drive, along with an Internet connection, and be able to update the WDO virus definitions. Can't do so with a CD.

I have used Windows Defender Off line on my computers using Brinks Tutorials and have had no problems. That doesn't mean it's the proper tool for every problem.
I was just wondering why I don't see it recommended by Security Experts anymore.

The incidence of Rootkit infested computers borked by WDO is not encouraging.

IMO that has made some malware advisors gun-shy.

Thanks. I will heed you gun shy.

I payed for the avast rescue disk ($10) as I wanted to support the company since I had used their free version.

Anyways, its a great tool and does scan the registry like stated before, and allows you to easily update the definitions.
I like it. Never had to use it thankfully on my machine. But others, it works quite well.