How does one effectively use the "Companies to exclude" option on Advertisements?

Kind of half of a question (the other part being "can we get this elsewhere too?) But I noticed a option to exclude companies in ads.

One assumes that this would work with the ads you get even when ads are reduced.

As such

I'm wondering how this works, how one identifies the companies in an ad, and how one can effectively use this to curate the ads one sees on the site (and broader Stack Exchange network, should we be graced with this option too - feature request is here for network wide support.)