It's never throwing your ballot in the garbage though. I used to think the same way, but every vote on the left, even if for the lesser evil, even if they lose, moves the conversation to the left. When we all stay home you get maga nutjobs stealing the show running unchecked.

Last thing is that gerrymandered states are the EASIEST to upset by increasing voter turnout. To gerrymander effectively you have to put your opponent in dense areas they'll win by a large margin, then spread your side so that you barely win the rest of the districts. That means that a 5% increase in votes on the left can take you from a loss to a nearly complete victory in a gerrymandered state.

Vote splitting on the other hand is a trickier beast, but in the end if all the left votes go to a moderate then that gives the left a lot of leverage because if the moderate candidate doesn't bend to the left then they'll lose the next election.

Always vote.