Can someone explain why the percentage of NULL column rows is useful/interesting?

What problem is it trying to solve?

Thanks

Since you've had no replies so far I'll just tell you what I know. The interface you're using is the right one, and you appear to be using it correctly...

Thanks, this is a great article that's opened an area I've never really explored before. However, it's not really working the way I'd expected. I have a lightly used, dedicated...

Definitely want one (even if it is April 1).