So about the only allowed form of advertising is mail addressed to "Occupant" sent to every postal address that is in the jurisdiction the office represents?
Nearly everything else will generally only reach a subset of the voters, and that subset will have known demographic differences from the overall voter demographics for the jurisdiction.
Run an ad at in the 8-8:30 PM Sunday slot on every FOX TV station in a state, for example, and you'll get quite a different demographic than if you ran an ad on those same stations on Sunday afternoon. The first ad would be during "The Simpsons" and the second would probably be during an NFL football game.