The first is that the new structure will help users narrow down which adverts they actually want to see - which is what everyone wants, isn't it? All this restructuring will give you greater control over things. If you don't need ads about cat food, you can block them. If you don't want to know about a new credit card offer, you can turn them off. In their place, you'll get an ad you might be interested in, like pizza. We all love pizza.
Secondly, it will help Facebook - which is a free service - convince a bunch more advertisers to take up its services. Many free websites suffer from ad blockers undermining their main revenue stream; advertisers won't be inclined to pay for ad space if they realise most people who use your website use an ad blocker. By ensuring every advert on Facebook is actually visible - and unblockable - Facebook will do wonders for convincing advertisers to sign up.
"We also know there’s more work to do, and we’re continually listening to your feedback to make advertising better for everyone," said Bosworth, so if you don't like the sound of unblockable ads, go tell him.