After the victim grants approval, the attacker can use the saved Request Token to complete the authorization flow, and access whatever Protected Resources are exposed by the (honest) Consumer site as part of its service.
As I understand the attack, when complete, the attacker will be able to sign-in as normal to his (honest) Consumer account and, in so doing, be able to (indirectly) access the Protected Resources that the honest (Service Provider) exposes (through OAuth). In other words, it's not the User's Consumer site resources that are compromised (as the above text suggests), but rather their SP resources.
Separately, I think the recommended warning text would have users running for the hills if they understood it. Why not piggy-back on whatever accumulated wisdom users have for detecting a phish?