Because there is no official documantation yet about the “Coverage” Value in
the new Google AdSense Beta Interface here is an explanation from Engineer Guillaume, a Google Employee on the Google AdSense help forums.
Coverage is the percentage of ad unit impressions or queries that showed ads:

A coverage of 100% means that AdSense was always able to provide ads to match the content of the page (Content) or the query keywords (Search).
A coverage of less than 100% means that AdSense was not able to find ads for some ad units or search queries, which didn’t show ads as a result.

It seems that Coverage is a very interesting parameter to see if overall you could remove an Ad Unit without losing money.

Depending on your strategies to use Adsense Channels of course.

What do you make out of this metric?

Do you find it interesting and which conclusions do you draw from it?