If you have any preference at all between the two party nominees then you are not throwing away your vote. You are voting for that preference and your vote counts. If you think cheese pizza is bland and boring but you are allergic to orange spray tanned pepperoni then being the only person voting for pineapple is objectively a worse choice than voting for cheese, because by voting for pineapple you are increasing the chance of having disgusting orange spray tanned pepperoni shoved in your face.