My individual vote is unlikely to make a difference. But it's pretty easy to define relatively small voting blocs (i.e. farmers in Kansas) that would alter the results of elections if their voting behavior radically changed.

Perhaps a given Kansas voter is obstructing a policy or candidate you favor, and you would be pleased if he changed his vote. Wouldn't you be fully half as pleased if he merely abstained from voting? My intuition is that it is far more than twice as difficult to change a vote than to discourage a vote.