The Syndicate

That button is a somewhat new feature of the poll I believe. Also, it's more of a legacy feature that we've always done for fun, I imagine.

That said, Sloonei makes a good point that some people might accidentally vote while not being a participant in the game, and since there's not a way to remove your vote, having an option to move it to is useful.

Similarly, if a player subs out of a game with a vote on the board, having an option to move their vote to is useful.