But it's such a specific structure, clearly there was an objective in mind when it was imlpemented.
Actually, it does. If the party you are registered with thinks are a voter who might not make it to the polls, and this is a close/important election, then there is a good chance you will receive numerous calls and/or visits reminding you to go out and vote. However, if you show up on the list of people who have voted by mail OR if you appear on the registry of people who have already voted in person, then they will stop reaching out to offer rides and reminders.
It's hard to say how much impact it has, but presumably there's a degree of social pressure when people are seen wearing/posting all those "I voted today" stickers.