It's a signal that you're willing to give up your principles in exchange for what the candidate supports. So by voting for Kamala "most lethal military in the world" "the difference between me and Joe Biden is that I'm not Joe Biden" Harris, one helps Palestinians in the sense of giving them the security in knowledge that 100% of viable political parties and their supporters are A-OK with their slaughter. This is a buff.

First of all, in most democratic systems, funding is often decided by reaching a certain vote count. Second, in most functioning democracies, votes on stuff is not actually neatly split amongst party lines, so a different distribution of seats might change certain results on certain votes. Thirdly, often there's another vote threshold than 50%, in most democracies there's stuff like "you need 2/3 of the votes to change the constitution" or similar, at which point "how much you lose by" also matters.

And the most important of all is the categorical imperative/universalization. "What if everyone acted like you did?"

If everyone didn't vote because "it doesn't accomplish anything" then the result is that it doesn't accomplish anything, you will definitely lose. But if everyone did vote even if it "doesn't accomplish anything", then suddenly you might win the vote because everyone voted.