Without instant run-offs, voting for an alternative candidate is tantamount to voting for your worst of the two viable choices. In 2000, Gore would have won the US presidential election if not for Nader voters whose second choice was Gore.
Yes, the current voting system makes alternative candidates practically irrelevant. But I still think it's better to make a point and to vote for whom you prefer - it's your public statement. Voting for the "least of two evils" since "evil" is expected to win either way, sounds bad to me.
