It's not a good tool if one party is likely, but not guaranteed, to win without your vote, but is much worse than the other. You should only spoil your ballot if your constituency is has a large enough majority that your vote won't matter at all, or none of the parties are less bad than the others.
If you're voting on the single issue of Palestine in the US presidential elections (not the primaries), then no state has a large enough majority to justify as spoiled ballots, and one party wants to support a genocide while the other wants to discourage it (even if they're doing a crap job of it), so there is a least bad option to vote for.