It is neither the loss of time nor do they give profit directly. It actually pays off when you see any abusive content and want them to be removed from HubPages. There are hundreds of hubs being published everyday and the moderators cannot reach all of them even if they try 24 hours a day. So, to keep the quality of the site healthy, they started this feature.
It benefits you in one thing - a shiny accolade. Hop some hubs and report them if they're abusive. You'll soon see a purple accolade saying "froch contributes to the community by helping new users in the forums and/or voting/flagging inappropriate contents"