The news capsule allows you to add current news stories to your hubs. It helps your hubs content stay current. Google likes current and continually updated content and may send more traffic to your hubs.
The Link capsule allows you to add links to other hubs (yours and others). This helps your "Hub Karma" score and I think If you add your URL tracker to the links you can get a percentage of earnings of other hubbers for a short period if the visitor clicks their ads. Sorry I don't know all the details on this right off. For more info check out the help sections of HubPages.