The intent is to pound your name into a voters head. Build name recognition. Add enthusiasm to the campaign. It looks good and it can help. This is best done by professionals, although you can conduct issues surveys to find out how voters view different issues or how they are reacting to the campaign.
Radio is a different story.
Radio stations give a 15 percent commission to the agencies that purchase the ads for your campaign. Usually, that is enough compensation for the radio buyer, although some might request a small retainer on top. The ads can be produced by the radio stations themselves. I prefer to put a large quantity of commercials on one station, rather than spread the ads out over several stations. In Chicago, the cost of radio ads drop to about half 60 days prior to the election.