It literally lists countering ad-blocking as a use case.
Users like visiting websites that are expensive to create and maintain, but they often want or need to do it without paying directly. These websites fund themselves with ads, but the advertisers can only afford to pay for humans to see the ads, rather than robots. This creates a need for human users to prove to websites that they're human, sometimes through tasks like challenges or logins.
Early on when Google wasn't shit and Facebook was just coming out of the startup phase both of them had chat platforms based on XMPP (the OG federating protocol). For a few glorious moments everyone could chat with anyone through the corresponding XMPP endpoints. At some point they decided they can't be arsed anymore and shut off federation on their servers. They captured enough market and siloed their users.
There's 1 million % this will happen again. It's textbook EEE.
Well done on Mastodon admins for not cooperating with Facebook's strong arming tactics. Facebook's server will evolve into another walled garden, Mastodon federating with them will only help them.
Fuck them
Unfortunately what's going to happen in reality is that any non-standard ad consumption (including non consumption) will be flagged as fraudulent. "We cannot verify your activity, please disable your add-ons to continue".