Let's say you have printed up tens or hundreds of thousands of fake ballots. But to make them appear legitimate you have people marking and signing them with a pen. This process can be both time consuming and expensive for large numbers of ballots.

If you are trying to rig one race you only need to vote that race, and leave the rest of the ballot blank or "under voted". You only have to make one mark and sign the ballot (or envelope).

One result of this is that the fake ballots will have no effect on down-ballot races.