Someone downvoted, but this is the right answer. Maybe the phrasing should have been reversed. I'll do that here.

I live in California. My vote doesn't matter in that we know California will go blue. Therefore, I can vote my conscience and not vote for Biden because the threat of Trump is neutralized. If people voting for third parties in safe blue stats start trending, Dems will be forced to try to appeal to said voters (the possibility of a third party getting covered in a meaningful way is unlikely at present).

I used to live in Kansas. Kansas was always a red state. It seems like it's become pretty close there now. I would not vote my conscience in Kansas for this election. It's possible that it could be a swing state. The threat of Trump is too great to take the risk.